Random map object "Map" should not overwrite the existing "Map" keyword

[elexis]

In JS, a "Map" is an object like an Array, see ​https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map

But the random map generation JS library introduces an own "Map" prototype that holds all the essential information passed to C++.

It should be renamed to avoid not only the direct naming conflict, but also the order-of-execution issue (if some code would want to register a Map prototype before the file defining that prototype was loaded. The files are loaded in alphabetic order.).

[elexis]

In 20898:

Rename random map Map to RandomMap, so that it doesn't overwrite the native JS Map object, fixes #4961.