Changes the `make` function signature to take an options struct, which
additionally includes `watch: bool`. I intentionally am not exposing
this information to configure phase logic.
Also adds global zig cache to the compiler cache prefixes.
Closes#20600
This has been planned for quite some time; this commit finally does it.
Also implements file system watching integration in the make()
implementation for UpdateSourceFiles and fixes the reporting of step
caching for both.
WriteFile does not yet have file system watching integration.