feat(ai): move includeRawChunks into include setting as rawChunks

[AhmadYasser1]

Background

streamText and generateText have an experimental_include setting for controlling what data is included in step results (e.g., requestBody, responseBody). The includeRawChunks parameter on streamText serves a similar purpose but lives as a separate top-level option. This PR moves it into the unified experimental_include setting as rawChunks.

Summary

• Added rawChunks?: boolean option to the experimental_include setting in streamText
• Deprecated the top-level includeRawChunks parameter with @deprecated JSDoc pointing to the new setting
• experimental_include.rawChunks takes precedence when both are specified; the deprecated parameter continues to work as a fallback for backward compatibility
• Added 4 new tests covering the new setting and precedence behavior

Usage:

const result = streamText({
  model,
  prompt: 'test prompt',
  // New way (preferred):
  experimental_include: { rawChunks: true },
  // Old way (deprecated):
  // includeRawChunks: true,
});

Manual Verification

• All 298 stream-text tests pass
• Full ai package test suite passes (1,769 tests across 87 files)
• Lint, typecheck, and prettier all pass

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Closes #12132