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/linuxbsd/detect.py

@@ -44,8 +44,6 @@ def get_opts():
         BoolVariable("fontconfig", "Detect and use fontconfig for system fonts support", True),
         BoolVariable("udev", "Use udev for gamepad connection callbacks", True),
         BoolVariable("x11", "Enable X11 display", True),
-        BoolVariable("debug_symbols", "Add debugging symbols to release/release_debug builds", True),
-        BoolVariable("separate_debug_symbols", "Create a separate file containing debugging symbols", False),
         BoolVariable("touch", "Enable touch events", True),
         BoolVariable("execinfo", "Use libexecinfo on systems where glibc is not available", False),
     ]
@@ -69,26 +67,9 @@ def configure(env):
 
     ## Build type
 
-    if env["target"] == "release":
-        if env["optimize"] == "speed":  # optimize for speed (default)
-            env.Prepend(CCFLAGS=["-O3"])
-        elif env["optimize"] == "size":  # optimize for size
-            env.Prepend(CCFLAGS=["-Os"])
-
-        if env["debug_symbols"]:
-            env.Prepend(CCFLAGS=["-g2"])
-
-    elif env["target"] == "release_debug":
-        if env["optimize"] == "speed":  # optimize for speed (default)
-            env.Prepend(CCFLAGS=["-O2"])
-        elif env["optimize"] == "size":  # optimize for size
-            env.Prepend(CCFLAGS=["-Os"])
-
-        if env["debug_symbols"]:
-            env.Prepend(CCFLAGS=["-g2"])
-
-    elif env["target"] == "debug":
-        env.Prepend(CCFLAGS=["-g3"])
+    if env.dev_build:
+        # This is needed for our crash handler to work properly.
+        # gdb works fine without it though, so maybe our crash handler could too.
         env.Append(LINKFLAGS=["-rdynamic"])
 
     # CPU architecture flags.
@@ -383,7 +364,7 @@ def configure(env):
     if env["execinfo"]:
         env.Append(LIBS=["execinfo"])
 
-    if not env["tools"]:
+    if not env.editor_build:
         import subprocess
         import re