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/android/detect.py

@@ -46,7 +46,7 @@ def get_ndk_version():
 def get_flags():
     return [
         ("arch", "arm64"),  # Default for convenience.
-        ("tools", False),
+        ("target", "template_debug"),
     ]
 
 
@@ -114,20 +114,6 @@ def configure(env):
     env.Append(CCFLAGS=target_option)
     env.Append(LINKFLAGS=target_option)
 
-    # Build type
-
-    if env["target"].startswith("release"):
-        if env["optimize"] == "speed":  # optimize for speed (default)
-            # `-O2` is more friendly to debuggers than `-O3`, leading to better crash backtraces
-            # when using `target=release_debug`.
-            opt = "-O3" if env["target"] == "release" else "-O2"
-            env.Append(CCFLAGS=[opt])
-        elif env["optimize"] == "size":  # optimize for size
-            env.Append(CCFLAGS=["-Oz"])
-    elif env["target"] == "debug":
-        env.Append(LINKFLAGS=["-O0"])
-        env.Append(CCFLAGS=["-O0", "-g"])
-
     # LTO
 
     if env["lto"] == "auto":  # LTO benefits for Android (size, performance) haven't been clearly established yet.
@@ -168,7 +154,7 @@ def configure(env):
     env["AS"] = compiler_path + "/clang"
 
     # Disable exceptions and rtti on non-tools (template) builds
-    if env["tools"]:
+    if env.editor_build:
         env.Append(CXXFLAGS=["-frtti"])
     elif env["builtin_icu"]:
         env.Append(CXXFLAGS=["-frtti", "-fno-exceptions"])