[api-extractor] Classify arrow functions as function kind in the doc model exports.

[bartvandenende-wm]

Summary

Classify arrow functions as function kind in the doc model exports.

Related issue ticket #1629

Details

The current behaviour of api-extractor is to classify arrow functions as variable kind. Even though syntactically correct, semantically (for documentation & usage purposes) this doesn't make any sense - and worse - it invalidates any documentation effort in the docstrings related to parameter descriptions, return types etc.

This PR modifies the doc-model generation to identify arrow functions in the variable declarations and processes them as function kinds instead.

Example code

/**
 * Demo log function
 * @param message - log message
 * @public
 */
export const log = (message: string): void => {console.log(message)}

doc model exports
Previous behaviour

{
  "kind": "Variable",
  "canonicalReference": "sample-lib!log:var",
  "docComment": "/**\n * Demo log function\n *\n * @param message - log message\n */\n",
  "excerptTokens": [
    {
      "kind": "Content",
      "text": "log: "
    },
    {
      "kind": "Content",
      "text": "(message: string) => void"
    }
  ],
  "fileUrlPath": "src/index.ts",
  "isReadonly": true,
  "releaseTag": "Public",
  "name": "log",
  "variableTypeTokenRange": {
    "startIndex": 1,
    "endIndex": 2
  }
}

New behaviour

  {
    "kind": "Function",
    "canonicalReference": "sample-lib!log:function(1)",
    "docComment": "/**\n * Demo log function\n *\n * @param message - log message\n */\n",
    "excerptTokens": [
      {
        "kind": "Content",
        "text": "log: (message: "
      },
      {
        "kind": "Content",
        "text": "string"
      },
      {
        "kind": "Content",
        "text": ") => "
      },
      {
        "kind": "Content",
        "text": "void"
      }
    ],
    "fileUrlPath": "src/index.ts",
    "returnTypeTokenRange": {
      "startIndex": 3,
      "endIndex": 4
    },
    "releaseTag": "Public",
    "overloadIndex": 1,
    "parameters": [
      {
        "parameterName": "message",
        "parameterTypeTokenRange": {
          "startIndex": 1,
          "endIndex": 2
        },
        "isOptional": false
      }
    ],
    "name": "log"
  }

How it was tested

manual testing

Impacted documentation

N/A