#3598 Navigator and encoding stream global shape parity

[andrewtdiz]

Refs #3598

Summary

• Exposes Navigator as a global constructor shape for the existing globalThis.navigator singleton, including constructor/prototype identity, instanceof Navigator, and Node-like illegal construction.
• Splits TextEncoderStream and TextDecoderStream allocation so each instance keeps the correct constructor identity, class id, prototype constructor, and instanceof behavior while preserving the existing readable/writable stub shape.
• Adds deterministic Node baseline fixtures for navigator and encoding stream constructor/instance identity.
• Documents URLPattern as intentionally absent while Perry advertises a Node 22 target.

Verification

• git fetch origin main and git merge-base --is-ancestor origin/main HEAD returned success.
• cargo fmt --check
• cargo check -q -p perry-runtime -p perry-hir -p perry-codegen
• cargo test -q -p perry-runtime navigator_global_constructor_identity_shape -- --nocapture
• cargo test -q -p perry-runtime text_encoding_stream_globals_construct_readable_writable_shape -- --nocapture
• Node baselines for:
  • test-parity/node-suite/globals/navigator-constructor-identity.ts
  • test-parity/node-suite/stream/web/text-encoding-stream-constructor-identity.ts
• git diff --check

I also accidentally invoked ./run_parity_tests.sh --help; it entered the broad release-build parity path, so I stopped it before fixture output per the bounded-verification coordination note.

Remaining Work

• URLPattern stays absent in this PR; adding the global and parser should be handled when/if Perry targets Node 24+ semantics.
• Encoding streams still expose only the modest constructor/prototype/instance/readable/writable shape here; full transform encode/decode stream behavior is left for a dedicated follow-up.
• This PR does not touch the URL/URLSearchParams/TextEncoder/TextDecoder constructor-exposure slice from draft PR Expose URL and encoding globals for #3598 #3631 or the queueMicrotask/Promise FIFO branch.