Restore macOS build and update Node toolchains to v22

[philippnormann]

This PR restores macOS build support (which had been untested) and updates all Node toolchains to v22, as the older binaries are no longer downloadable. Additional changes include:

• Making build.sh executable and standardizing the output ZIP name
• Updating the macOS build configuration (.mozconfig) for compatibility
• Fixing Taskgraph wiring so toolchain dependencies resolve correctly

Verified locally:

• Built on macOS using build.sh -p with Playwright integration
• Successfully ran a Playwright smoke test on the compiled macOS binary

[cla-assistant]

All committers have signed the CLA.