[flow][refactor] Restore readability of dispatch.rs and subtyping_kit.rs 4/n: property and spread patterns

Summary:
Move object, instance, array, and property-key structure into dispatch patterns. Match indexed objects directly for dictionary values and union indexed access, preserving the remaining semantic guards.

Changelog: [internal] Simplify property and spread dispatch patterns.

Reviewed By: panagosg7

Differential Revision: D126949166

fbshipit-source-id: db4bad345986fba6185d53aa3814cbbfa1a5c9cc

Author: SamChou19815