Sync to upstream/release/527

[zeux]

• Fix type checker assertions on some valid code
• Type checker now correctly applies the expected shape of a table literal in certain cases (fixes Roblox Studio has major type system regressions, breaking developer-facing code for the Pract library. #483)
• Fix certain cases of generic types leaking to outside scopes (fixes Roblox Studio latest release has issues with nested generic types leaking #484)
• Fix type checking of generic functions in certain cases when not all function arguments/returns were annotated
• Bytecode optimizer can now inline functions and unroll loops with nested closures at -O2
• Improve bytecode optimizations for code that returns a type-cast local (return a :: type)