SCons: Improve debug symbol logic & cleanup

[Repiteo]

Depends on #91847

This PR improves the debugsymbol logic overall in a number of ways:

• Ensures that debugsymbol files will be cleaned up when passing --clean to SCons. Logic to support something similar already existed in the Windows SCSub via arrange_program_clean, but that's now been migrated to methods.py & refactored as a universal environment function.
• The original debugsymbol functions in platform_*_builders.py have been migrated to their respective SCSub, being cleaned up in the process. Consequently, the original files have been removed, as they only had that single function & the files themselves became redundant once subprocess dependencies were removed¹.
• Windows now correctly checks for both debug_symbols and separate_debug_symbols before attempting separation; previously, it only checked for the former. EDIT: Working as intended.
• Windows now checks if objcopy and strip exist in detect.py instead of SCSub, and throws a proper error if they're missing. This allows pulling their MinGW paths only once & will alert the user to issues prior to building instead of at the very last second.
• Windows now assigns .debugsymbol extension to program stem instead of the existing name (.exe.debugsymbols → .debugsymbols). This matches the naming scheme of the other Windows program files that require explicit cleanup (.ilk, .exp, .pdb, .lib).

Footnotes

1. SCons: Remove run_in_subprocess & subprocess_main dependencies #89393 ↩

[bruvzg]

Windows now correctly checks for both debug_symbols and separate_debug_symbols before attempting separation; previously, it only checked for the former.

This was intentional, MinGW build should check for executable size and force debug symbols if it's too large (see #79875), but seems like the logic is already broken by #85319, the following two lines were likely accidentally removed during rebase:

    # Force separate debug symbols if executable size is larger than 1.9 GB.
    if env["separate_debug_symbols"] or os.stat(target[0]).st_size >= 2040109465:

[Repiteo]

It seems to still only look for prefixed executables, so probably not fixed.

It only looks for a prefixed executable when checking if Windows is a supported platform, ensuring no false positives. If Windows is supported & selected for building, the mingw_prefix bin folder is prepended to the SCons Environment's path

[bruvzg]

If Windows is supported & selected for building, the mingw_prefix bin folder is prepended to the SCons Environment's path

I have missed that it's checking for env to set prefix, not sure if it is the best way for code readability, but should work indeed.

[akien-mga]

Expanded this PR slightly to include a fix for #91710, as it was already dealing with get_mingw_tool & general Windows detect.py cleanup.

I'd prefer it on a standalone PR to fix the regression only. Build system changes have a high risk of breaking specific configs so I prefer we first fix the known issues, before adding potential new ones by fast tracking an enhancement PR.

[Repiteo]

That's a really good point. Removed the fix from this PR & migrated the code to #91734 instead.

[Repiteo]

Changing to a draft now that this is a dependency of #91847.