[memoryprofiler] Add CSS class to parent div

[shreyas-omkar]

Add a CSS class to the main parent div of the memory profiler UI.

Currently, the profiler's container div is created with no ID or class, making it impossible to target with CSS. This is problematic for developers (like in the original issue) who run their application in full-screen, as the profiler UI gets hidden with no way to adjust its z-index.

This change adds the class emscripten-memory-profiler-container to the div upon its creation in library_memoryprofiler.js.

This allows developers to easily style the profiler. For example:

<style>
  .emscripten-memory-profiler-container {
    z-index: 9999;
  }
</style>

Fixes: #20115

[shreyas-omkar]

@sbc100 Please review the changes.

[shreyas-omkar]

Sure I will.

[shreyas-omkar]

Hi @sbc100 I have removed the ChangeLog.