SCons: Unify tools/target build type configuration

Implements https://github.com/godotengine/godot-proposals/issues/3371.

New `target` presets
====================

The `tools` option is removed and `target` changes to use three new presets,
which match the builds users are familiar with. These targets control the
default optimization level and enable editor-specific and debugging code:

- `editor`: Replaces `tools=yes target=release_debug`.
  * Defines: `TOOLS_ENABLED`, `DEBUG_ENABLED`, `-O2`/`/O2`
- `template_debug`: Replaces `tools=no target=release_debug`.
  * Defines: `DEBUG_ENABLED`, `-O2`/`/O2`
- `template_release`: Replaces `tools=no target=release`.
  * Defines: `-O3`/`/O2`

New `dev_build` option
======================

The previous `target=debug` is now replaced by a separate `dev_build=yes`
option, which can be used in combination with either of the three targets,
and changes the following:

- `dev_build`: Defines `DEV_ENABLED`, disables optimization (`-O0`/`/0d`),
  enables generating debug symbols, does not define `NDEBUG` so `assert()`
  works in thirdparty libraries, adds a `.dev` suffix to the binary name.

Note: Unlike previously, `dev_build` defaults to off so that users who
compile Godot from source get an optimized and small build by default.
Engine contributors should now set `dev_build=yes` in their build scripts or
IDE configuration manually.

Changed binary names
====================

The name of generated binaries and object files are changed too, to follow
this format:

`godot.<platform>.<target>[.dev][.double].<arch>[.<extra_suffix>][.<ext>]`

For example:
- `godot.linuxbsd.editor.dev.arm64`
- `godot.windows.template_release.double.x86_64.mono.exe`

Be sure to update your links/scripts/IDE config accordingly.

More flexible `optimize` and `debug_symbols` options
====================================================

The optimization level and whether to generate debug symbols can be further
specified with the `optimize` and `debug_symbols` options. So the default
values listed above for the various `target` and `dev_build` combinations
are indicative and can be replaced when compiling, e.g.:

`scons p=linuxbsd target=template_debug dev_build=yes optimize=debug`
will make a "debug" export template with dev-only code enabled, `-Og`
optimization level for GCC/Clang, and debug symbols. Perfect for debugging
complex crashes at runtime in an exported project.

platform/windows/detect.py

@@ -173,17 +173,7 @@ def get_opts():
             "Targeted Windows version, >= 0x0601 (Windows 7)",
             "0x0601",
         ),
-        BoolVariable(
-            "debug_symbols",
-            "Add debugging symbols to release/release_debug builds",
-            True,
-        ),
         EnumVariable("windows_subsystem", "Windows subsystem", "gui", ("gui", "console")),
-        BoolVariable(
-            "separate_debug_symbols",
-            "Create a separate file containing debugging symbols",
-            False,
-        ),
         (
             "msvc_version",
             "MSVC version to use. Ignored if VCINSTALLDIR is set in shell env.",
@@ -330,32 +320,12 @@ def setup_mingw(env):
 def configure_msvc(env, vcvars_msvc_config):
     """Configure env to work with MSVC"""
 
-    # Build type
-    if env["target"] == "release":
-        if env["optimize"] == "speed":  # optimize for speed (default)
-            env.Append(CCFLAGS=["/O2"])
-            env.Append(LINKFLAGS=["/OPT:REF"])
-        elif env["optimize"] == "size":  # optimize for size
-            env.Append(CCFLAGS=["/O1"])
-            env.Append(LINKFLAGS=["/OPT:REF"])
+    ## Build type
+
+    # TODO: Re-evaluate the need for this / streamline with common config.
+    if env["target"] == "template_release":
         env.Append(LINKFLAGS=["/ENTRY:mainCRTStartup"])
 
-    elif env["target"] == "release_debug":
-        if env["optimize"] == "speed":  # optimize for speed (default)
-            env.Append(CCFLAGS=["/O2"])
-            env.Append(LINKFLAGS=["/OPT:REF"])
-        elif env["optimize"] == "size":  # optimize for size
-            env.Append(CCFLAGS=["/O1"])
-            env.Append(LINKFLAGS=["/OPT:REF"])
-
-    elif env["target"] == "debug":
-        env.AppendUnique(CCFLAGS=["/Zi", "/FS", "/Od", "/EHsc"])
-        env.Append(LINKFLAGS=["/DEBUG"])
-
-    if env["debug_symbols"]:
-        env.AppendUnique(CCFLAGS=["/Zi", "/FS"])
-        env.AppendUnique(LINKFLAGS=["/DEBUG"])
-
     if env["windows_subsystem"] == "gui":
         env.Append(LINKFLAGS=["/SUBSYSTEM:WINDOWS"])
     else:
@@ -491,31 +461,10 @@ def configure_mingw(env):
     if env["use_llvm"] and not try_cmd("clang --version", env["mingw_prefix"], env["arch"]):
         env["use_llvm"] = False
 
-    if env["target"] == "release":
+    # TODO: Re-evaluate the need for this / streamline with common config.
+    if env["target"] == "template_release":
         env.Append(CCFLAGS=["-msse2"])
-
-        if env["optimize"] == "speed":  # optimize for speed (default)
-            if env["arch"] == "x86_32":
-                env.Append(CCFLAGS=["-O2"])
-            else:
-                env.Append(CCFLAGS=["-O3"])
-        else:  # optimize for size
-            env.Prepend(CCFLAGS=["-Os"])
-
-        if env["debug_symbols"]:
-            env.Prepend(CCFLAGS=["-g2"])
-
-    elif env["target"] == "release_debug":
-        env.Append(CCFLAGS=["-O2"])
-        if env["debug_symbols"]:
-            env.Prepend(CCFLAGS=["-g2"])
-        if env["optimize"] == "speed":  # optimize for speed (default)
-            env.Append(CCFLAGS=["-O2"])
-        else:  # optimize for size
-            env.Prepend(CCFLAGS=["-Os"])
-
-    elif env["target"] == "debug":
-        env.Append(CCFLAGS=["-g3"])
+    elif env.dev_build:
         # Allow big objects. It's supposed not to have drawbacks but seems to break
         # GCC LTO, so enabling for debug builds only (which are not built with LTO
         # and are the only ones with too big objects).