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.

misc/dist/html/editor.html

@@ -411,7 +411,7 @@
 			}
 		}
 	//]]></script>
-	<script src="godot.tools.js"></script>
+	<script src="godot.editor.js"></script>
 	<script>//<![CDATA[
 
 		var editor = null;
@@ -706,7 +706,7 @@
 				displayFailureNotice('WebGL not available');
 			} else {
 				setStatusMode('indeterminate');
-				editor.init('godot.tools').then(function() {
+				editor.init('godot.editor').then(function() {
 					if (zip) {
 						editor.copyToFS("/tmp/preload.zip", zip);
 					}

misc/dist/html/manifest.json

@@ -3,7 +3,7 @@
   "short_name": "Godot",
   "description": "Multi-platform 2D and 3D game engine with a feature-rich editor (Web edition)",
   "lang": "en",
-  "start_url": "./godot.tools.html",
+  "start_url": "./godot.editor.html",
   "display": "standalone",
   "theme_color": "#202531",
   "icons": [