feat(biome_graphql_parser): parse schema extension

[vohoanglong0107]

Summary

Parse GraphQL schema extensions. This is a small case, as almost all parsing logic was handled by a previous PR focusing on parsing schema definition.
The schema extension syntax defined the ungrammar was needlessly complicated, this PR also simplifies the syntax.
Depends on #2841

Test Plan

All tests should pass.

[codspeed-hq]

CodSpeed Performance Report

Merging #2842 will not alter performance

_{Comparing vohoanglong0107:feat-graphql-schema-extension (ce24e8d) with main (b1e7be6)}

Summary

✅ 99 untouched benchmarks