Replace cabal project parsing with parsec implementation

The new parser replicates the grammar of the legacy parser while providing
better error reporting and more maintainable code structure. The fallback
strategy ensures smooth transition while the legacy parser is phased out.

The flag `--project-file-parser` allows you to select which project file
parser to use.

* `legacy` - the old parser (will be removed in a future release)
* `default` - the default parser (uses `fallback` unless compiled with `-f+legacy-comparison`)
* `parsec` - the new parser using Parsec
* `fallback` - the new parser using Parsec, but falling back to the old parser if it fails
* `compare` - the new parser using Parsec, but comparing the results with the old parser

When `cabal-install` is compiled, then the `-f+legacy-comparision` flag
can be passed which changes the default parser mode to `compare`.

Fixes #6101 #7748 #10611