typescript-angular: single request parameter documentation

Created by: alexrashed

Fixes #5307 (closed) If useSingleRequestParameter is activated for the Angular generator, a JSDoc comment is added to the generated request parameter interface members (if a description is given in the spec).

Previously:

export interface ExampleRequestParams {
  test: string;
}

With this PR:

export interface ExampleRequestParams {
  /** An example documentation of the request parameter test. */
  test: string;
}

PR checklist

• Read the contribution guidelines.
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Technical commitee

@TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @nicokoenig (2018/09) @topce (2018/10) @akehir (2019/07) @petejohansonxo (2019/11) @amakhrov (2020/02)