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/web/detect.py

@@ -47,7 +47,7 @@ def get_opts():
 def get_flags():
     return [
         ("arch", "wasm32"),
-        ("tools", False),
+        ("target", "template_debug"),
         ("builtin_pcre2_with_jit", False),
         ("vulkan", False),
         # Use -Os to prioritize optimizing for reduced file size. This is
@@ -77,26 +77,17 @@ def configure(env):
         sys.exit(255)
 
     ## Build type
-    if env["target"].startswith("release"):
-        if env["optimize"] == "size":
-            env.Append(CCFLAGS=["-Os"])
-            env.Append(LINKFLAGS=["-Os"])
-        elif env["optimize"] == "speed":
-            env.Append(CCFLAGS=["-O3"])
-            env.Append(LINKFLAGS=["-O3"])
 
-        if env["target"] == "release_debug":
-            # Retain function names for backtraces at the cost of file size.
-            env.Append(LINKFLAGS=["--profiling-funcs"])
-    else:  # "debug"
-        env.Append(CCFLAGS=["-O1", "-g"])
-        env.Append(LINKFLAGS=["-O1", "-g"])
+    if env.debug_features:
+        # Retain function names for backtraces at the cost of file size.
+        env.Append(LINKFLAGS=["--profiling-funcs"])
+    else:
         env["use_assertions"] = True
 
     if env["use_assertions"]:
         env.Append(LINKFLAGS=["-s", "ASSERTIONS=1"])
 
-    if env["tools"]:
+    if env.editor_build:
         if env["initial_memory"] < 64:
             print('Note: Forcing "initial_memory=64" as it is required for the web editor.')
             env["initial_memory"] = 64