GraphQL improvements

[RunDevelopment]

This PR resolves #1786

Changes to the GraphQL language definition:

1. Added missing keywords.
2. Fixed field names with arguments. (Small correction of Modify attr-name regex to include fields with arguments #1711)
3. Added missing | operator for unions.
4. Added highlighting of fragments.
5. Added highlighting for class-names after type definition keywords.
6. Added constants. These match all identifiers which do not contain lower case letters (ID is the only exception here). This is intended to highlight enum values.

Examples

Better attr-name:

New: Highlighting of fragments

New: Highlighting of constants/enum values (detected using naming conventions)

[MichalLytek]

@RunDevelopment
Is there any ETA or some blockers for this feature?
I would love to release it ASAP and update Prism in Docusaurus for my docs page 😃