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
* improve error message when build manifest file is missing
* update std.zig.Ast to support ZON
* Compilation.AllErrors.Message: make the notes field a const slice
* move build manifest parsing logic into src/Manifest.zig and add more
checks, and make the checks integrate into the standard error
reporting code so that reported errors look sexy
closes#14290
