build: install AccessKit/ANGLE deps and fix build script arguments

[Naruto]

Description

Godot 4.7 links two prebuilt SDKs that are not part of the engine source tree: AccessKit (screen reader support) and ANGLE (the OpenGL ES rendering driver). When they are missing, scons only prints a warning and silently disables those drivers, so the editor/templates we build lack features the official Godot builds ship with:

WARNING: The screen reader support driver requires dependencies to be installed.
WARNING: The ANGLE rendering driver requires dependencies to be installed.

build.sh / build.ps1 now install them before invoking scons, using the installers from the godot/ checkout so the dependency versions always match the engine revision being built. A new deps=<yes|no> option (default yes) controls this; already-installed dependencies are skipped, mobile/web platforms use neither, and ANGLE is additionally skipped on Linux.

While verifying the 4.7 build, a few build-script defects surfaced and are fixed here as well:

• build.sh ignored cpus= and always passed the default value to scons -j ($build_default_opts[cpus] instead of ${opts[cpus]}).
• build.ps1 seeded its scons argument string from an undefined $internal_opts (emitting an empty platform=) and then concatenated the whole string onto itself (+= with the full string).
• build.ps1 forwarded release-windows.ps1's strip=yes to scons instead of consuming it as a build-script option. It is now a recognized option, documented as a no-op on MSVC (debug info lives in a separate .pdb).
• .github/actions/setup-godot fetched ANGLE pinned at chromium/6601.2 (4.7 needs chromium/7219) and unpacked it outside build_deps. Those steps are removed since the build scripts now cover it; the Vulkan SDK and D3D12 steps are kept.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Verification

Verified on macOS (arm64) against godot @ 4.7 (v4.7.2.rc) and godot-cpp @ master:

Check	Result
./scripts/build.sh (custom module, target=editor)	Succeeds; both warnings gone, links with ANGLE_ENABLED
./scripts/build-extension.sh (GDExtension, api_version=4.7)	Succeeds
Built Godot.app: SpriteStudioPlayer2D / SSABResource registered and instantiable	OK
Re-running build.sh with dependencies present	Skips both downloads (no re-fetch)

Windows and Linux are not verified by an actual build; build.ps1 was checked by parser validation and a dry run of its scons argument assembly.

Notes

• Linking now emits duplicate symbol warnings for Rust symbols (rust_eh_personality, __rust_alloc, ...) shared between libssruntime, libssconverter and 4.7's new libaccesskit. The link succeeds; recorded here as a known 4.7 artifact.
• build.sh still carries a dead if [[ ${VERSION} =~ ^3\..* ]] branch for Godot 3.x. Left untouched to keep this change scoped.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules