* 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
* std.zig.parse is moved to std.zig.Ast.parse
* the new function has an additional parameter that requires passing
Mode.zig or Mode.zon
* moved parser.zig code to Parse.zig
* added parseZon function next to parseRoot function
