Refactor version macros and fix related bugs

The previous logic with VERSION_MKSTRING was a bit unwieldy, so there were
several places hardcoding their own variant of the version string, potentially
with bugs (e.g. forgetting the patch number when defined).

The new logic defines:

- VERSION_BRANCH, the main 'major.minor' version (e.g. 3.1)
- VERSION_NUMBER, which can be 'major.minor' or 'major.minor.patch',
  depending on whether the latter is defined (e.g. 3.1.4)
- VERSION_FULL_CONFIG, which contains the version status (e.g. stable)
  and the module-specific suffix (e.g. mono)
- VERSION_FULL_BUILD, same as above but with build/reference name
  (e.g. official, custom_build, mageia, etc.)
  Note: Slight change here, as the previous format had the build name
  *before* the module-specific suffix; now it's after
- VERSION_FULL_NAME, same as before, so VERSION_FULL_BUILD prefixed
  with "Godot v" for readability

Bugs fixed thanks to that:

- Export templates version matching now properly takes VERSION_PATCH
  into account by relying on VERSION_FULL_CONFIG.
- ClassDB hash no longer takes the build name into account, but limits
  itself to VERSION_FULL_CONFIG (build name is cosmetic, not relevant
  for the API hash).
- Docs XML no longer hardcode the VERSION_STATUS, this was annoying.
- Small cleanup in Windows .rc file thanks to new macros.

scene/main/http_request.cpp

@@ -121,7 +121,7 @@ Error HTTPRequest::request(const String &p_url, const Vector<String> &p_custom_h
 	}
 
 	if (!has_user_agent) {
-		headers.push_back("User-Agent: GodotEngine/" + String(VERSION_MKSTRING) + " (" + OS::get_singleton()->get_name() + ")");
+		headers.push_back("User-Agent: GodotEngine/" + String(VERSION_FULL_BUILD) + " (" + OS::get_singleton()->get_name() + ")");
 	}
 
 	if (!has_accept) {