Close gaps in functionality between annotation-processor and Java TypeSpec generator

[Alan Zimmer (alzimmermsft)]

Description

• Added @FormParam URL-encoded bodies using FORM_ESCAPER.
• Added header-collection expansion and correct dynamic-header precedence.
• Added optional/non-string path handling and collection-query semantics.
• Fixed unknown-length BinaryData, direct/sliced ByteBuffer, dynamic content types, JSON charset handling, and pre-serialized multipart bodies.
• Added type-based RequestContext and SSE listener wiring.
• Fixed response closure so eager responses close exactly once while streaming responses remain open.
• Added text, standard Base64, primitive, enum, list, map, and nested generic response decoding.
• Extended JsonSerializer.java, JsonWriter.java, and CoreUtils.java for typed collections, temporal values, decimals, enums, BinaryData, and ISO durations with day components.
• Fixed SSE response-body ownership in OkHttpHttpClient.java.
• Removed generated SuppressWarnings("cast"), enabled all previously disabled processor integration tests, aligned tests with processor beta.5/Core beta.12, and regenerated checked-in service implementations.
  Updated changelogs and added focused unit/integration coverage.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

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