Most of this migration was performed automatically with `zig fmt`. There
were a few exceptions which I had to manually fix:
* `@alignCast` and `@addrSpaceCast` cannot be automatically rewritten
* `@truncate`'s fixup is incorrect for vectors
* Test cases are not formatted, and their error locations change
These functions are problematic in light of dependencies because they
run and install, respectively, for the *owner* package rather than for
the *user* package. By removing these functions, the build script is
forced to provide the *Build object to associate the new step with,
making everything less surprising.
Unfortunately, this is a widely breaking change.
see #15079
