Allow both module.exports= and module.exports property assignments

[sandersn]

In Javascript, it's common both to assign to module.exports and to assign properties to module.exports:

module.exports = function A() {
  this.p = 1
}
module.exports.util = function() {
  return "Hooray, I'm useful! I'm having a wonderful time."
}

This should be treated as equivalent to the Typescript:

class A {
  p = 1
}
namespace A {
  export function util() {
    return "Looking for static public abstract readonly internal classes? Why not Typescript?"
  }
}
export = A

This PR merges module.exports assignments with module.exports property assignments to produce a symbol structure similar to the Typescript binding. Unfortunately, since we're merging values, the normal merging code will not work. After binding the first example, the file's exports have the following structure:

exports: {
  "export=": { valueDeclaration: module.exports = function ...
  "util": { valueDeclaration: module.exports.util = function ...
}

Then when the checker encounters var x = require(...), it looks up the file's exports and retrieves the "export=" entry.

This PR copies the other entries of exports over to export='s exports:

exports: {
  "export=": { 
    valueDeclaration: module.exports = function ..., 
    exports: {
      util: { valueDeclaration: ... }
    }
  },
  util: { valueDeclaration: ... }
}

This makes the export= symbol equivalent to the merged typescript in the second example.
Then when the checker asks for the type of this symbol, it can get the property assignments by looking at the exports of the symbol.

Since the same property can be assigned in both export= and property assignments, some unioning code is also required:

module.exports = { both: 1 }
module.exports.both = 'both: string | number'

In addition, if the module.exports = 1 (or any primitive type), then subsequent assignments will be ignored, so none of the property assignments should show up as exports either.

Fixes #22461