[typescript-fetch] Document request-parameter interfaces and fix parameter isDeprecated

[babariviere]

Fixes #24511

What is this PR about?

When useSingleRequestParameter is enabled, typescript-fetch bundles an operation's parameters into a generated XxxRequest interface. Those interfaces were emitted with bare properties: no JSDoc descriptions, and no @deprecated even when a parameter is marked deprecated: true in the spec.

#11522 / #11523 previously added @deprecated for operations and model properties, but operation parameters were never covered, and a copy-constructor bug made parameter deprecation impossible to detect regardless of template.

This PR does two things:

1. Fixes isDeprecated always being false on parameters. DefaultCodegen.fromParameter correctly sets CodegenParameter.isDeprecated from the OpenAPI deprecated field, but TypeScriptFetchClientCodegen.ExtendedCodegenParameter's copy constructor wrapped the parameter and copied ~70 fields while omitting isDeprecated, silently resetting it to false. (The vendorExtensions field is copied, which is why only vendor-extension workarounds surfaced deprecation before.) The one-line fix copies isDeprecated through, matching what the operation and model wrappers already do.
2. Documents request-parameter interfaces in apis.mustache with JSDoc (description and @deprecated when the parameter is deprecated), consistent with the model interface template.

Example

Given a query parameter marked deprecated: true:

parameters:
  - name: q
    in: query
    description: Free-text search query.
    schema: { type: string }
  - name: legacyId
    in: query
    deprecated: true
    description: Deprecated. Use id instead.
    schema: { type: string }

Before:

export interface ListItemsRequest {
    q?: string;
    legacyId?: string;
}

After:

export interface ListItemsRequest {
    /**
     * Free-text search query.
     */
    q?: string;
    /**
     * Deprecated. Use id instead.
     * @deprecated
     */
    legacyId?: string;
}

PR checklist

• Read the contribution guidelines.
• Opened an issue first ([BUG][typescript-fetch] @deprecated JSDoc missing on operation parameters (parameter isDeprecated always false) #24511) describing the bug with a reproducer.
• Ran ./bin/generate-samples.sh bin/configs/typescript-fetch-*.yaml to update the samples (additive JSDoc only).
• Added a unit test (TypeScriptFetchClientCodegenTest#testDeprecatedParameter).
• Copied the technical committee to review.

cc typescript-fetch technical committee: @macjohnny @topce @amakhrov @davidgamero @joscha

---

Summary by cubic

Fixes missing deprecation flags and adds JSDoc to request-parameter interfaces in typescript-fetch when useSingleRequestParameter is enabled. Deprecated parameters now render @deprecated, and generated request interfaces include descriptions; samples were regenerated to reflect the changes.

• Bug Fixes

  • Copy isDeprecated into ExtendedCodegenParameter so deprecated params in XxxRequest interfaces include @deprecated; adds TypeScriptFetchClientCodegenTest#testDeprecatedParameter.

• New Features

  • Emit JSDoc for properties in XxxRequest interfaces via apis.mustache (description and @deprecated when applicable); regenerates typescript-fetch samples.

^{Written for commit 69e0630. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[macjohnny]

thanks for the contribution