[#3598] Add FormData constructor and mutator parity

[andrewtdiz]

Refs #3598

Summary

• add new FormData() lowering plus native FormData registry allocation
• wire string-valued FormData append, set, delete, has, get, getAll, entries, keys, values, and forEach through typed and any-typed fetch handle dispatch
• expose deterministic FormData constructor/prototype name/length metadata and add FormData to the fetch/node-fetch API manifest declarations
• add a focused parity fixture for constructor/prototype/mutator/iteration/forEach ordering

Verification

• cargo fmt --check
• node --experimental-strip-types test-parity/node-suite/fetch/form-data/constructor-mutators.ts
• cargo check -p perry-stdlib -p perry-runtime -p perry-codegen -p perry-hir
• cargo build -p perry -p perry-runtime -p perry-stdlib
• PERRY_ALLOW_UNIMPLEMENTED=1 ./target/debug/perry test-parity/node-suite/fetch/form-data/constructor-mutators.ts -o /tmp/perry_formdata_constructor_mutators && /tmp/perry_formdata_constructor_mutators matched the Node baseline; the fetch sidecar auto-optimize build was bounded/stopped after dependency build contention and Perry fell back to prebuilt libs before linking/running the fixture.
• Attempted ./run_parity_tests.sh --suite node-suite --module fetch, stopped while it was sitting in release-build contention without useful fixture output.

Remaining Fetch/FormData Work

• File/Blob-valued FormData entries are not implemented in this registry; values are currently stored/coerced as strings.
• Multipart FormData parsing/serialization and filename/content-type metadata remain follow-up work.
• Broader Body method expansion beyond the locally supported fetch registry is intentionally left out of this PR.
• This does not change globalThis.fetch value exposure; that remains separate from draft PR fix(fetch): expose globalThis fetch value #3632.