Use a temp file for ARCOM to fix command line too long errors

[aaronfranke]

With my Godot fork, the added C++ modules are enough to push godot-cpp over the limit. The total length of all C++ files concatenated into the argument list is over 133 thousand bytes, which exceeds the 128 KiB limit of Linux argument lists:

This PR fixes the problem on godot-cpp's side by adding ARCOM, which allows SCons to write the arguments to a file, and then pass that file to ar, rather than trying to put everything into command line arguments.

I have verified that this works, because I pointed the failing dimensions-4.8 branch at aaronfranke/godot-cpp with branch 4.5-arcom-command-length, and now the "Linux / Editor w/ Mono (target=editor)" CI job that includes godot-cpp succeeds: https://github.com/godot-dimensions/godot/actions/runs/30248252906/job/89922634667

Note that this isn't a godot-dimensions specific issue: the same problem would've occurred with Godot itself in a matter of years as the engine size grows over time. My godot-dimensions fork merely encountered the problem sooner.

This should be cherry-picked to past branches. The cherry-picking is beneficial to forks. I have branches ready for this, here is the 4.5 branch: https://github.com/aaronfranke/godot-cpp/tree/4.5-arcom-command-length EDIT: I will update this branch with this PR's updated contents soon.

Corresponding engine PR: https://github.com/godotengine/godot/pull/96407/changes

Supersedes #1731

[dsnopek]

As mentioned at the GDExtension team meeting, it would be good to check if we need the changes to methods.py from the upstream PR (in godot-cpp, that code is in tools/my_spawn.py)

[aaronfranke]

Updated the PR to closely mirror the engine code, and use a unified place for the ARCOM logic across all platforms (just like the engine code does - ARCOM for all platforms, plus backslash-escaping code for Windows).