Add support for @catch on fragments/queries/mutations and aliased inline fragments

[captbaritone]

@catch was originally conceived as a means for handling field errors, so we built it as a directive on fields. However, as the design evolved we opted to make it additionally catch any errors nested within it. With this newer approach, there’s no reason to limit @catch to just fields. Any GraphQL construct which gets read as a concrete value should be able to operate as a @catch boundary.

This PR adds support for marking fields/queries/mutations and aliased fragments as @catch boundaries. This means:

1. Their value will be read out as either nullable or a Result type
2. @semanticNonNull values nested within the fragment/operation/mutation/aliased fragment will be typed using their semantic type (non-nullable)

One particularly nice thing this enables is that it allows @catch to act as a non-destructive alternative to @throwOnFieldError.

Additional Bug Fixes

Along the way I noticed and fixed a few bugs:

1. Semantic nullability was not respected within inline fragments nested within @catch or @throwOnFieldError
2. Errors that bubbled up to a @catch(to: NULL) directive would not actually cause the value to become null.

[facebook-github-bot]

@captbaritone has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@captbaritone merged this pull request in 7c9aebb.