feat: streamline using Reclient for Chromium

[codebytere]

Enables building stock Chromium more simply.

Patches are applied now upon sync when targeting Chromium, with reduced area for failure with pinned EngFlow/reclient-configs sha.

[dsanders11]

Has this been tested on Windows? I have a feeling we want to use depotSpawnSync to ensure that the depot_tools managed Python 3 gets used there.

[codebytere]

@dsanders11 no, i've only done this on posix so far! good call though, i think you're right 😅