The `driver_ast_parser` tool is now able to parse constants alongside with
structs. This is done by adding a new `constants` field in the JSON input, and
a `constants` field in the JSON output. This will be used later to detect
changes in constants between driver versions.
Also, the parser's `structs` argument was renamed to `input` to account for
both structs and constants.
PiperOrigin-RevId: 792677998
This is an improvement from just comparing the fields of top-level structs.
As a part of this, we handle anonymous records and arrays as well.
PiperOrigin-RevId: 657652481