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
* `doc/langref` formatting
* upgrade `.{ .path = "..." }` to `b.path("...")`
* avoid using arguments named `self`
* make `Build.Step.Id` usage more consistent
* add `Build.pathResolve`
* use `pathJoin` and `pathResolve` everywhere
* make sure `Build.LazyPath.getPath2` returns an absolute path