Fix issues in IE9 compatible browser #4624

[gnh1201]

What does this PR do?

• Fix issues in IE9 compatible browser #4624

Where should the reviewer start?

• src/js/core/env.js
  • When rendering the summernote editor in IE9 (IE9 compatible browser), $popover (or this.$popover) should not be null. (Based on summernote commit https://github.com/summernote/summernote/commit/1521019b4479393f1077083f4445e3ea61d73297.)
  • The issue arose due to the lack of a join method in the CanvasPixelArray prototype, so I have added a check for this prototype.
• src/js/module/Editor.js
  • When applying styles such as bold, underline, and italic in IE9 (IE9 compatible browser) there should be no errors. (Based on summernote version 0.8.18)

How should this be manually tested?

• Here's where this change will be applied. If needed, it can be executed and tested. There's no separate installation process required: https://github.com/gnh1201/welsonjs

Any background context you want to provide?

• This is a patch related to a browser that is compatible with IE9 specifications, not meant for general users but for industrial purposes. Unlike IE9 for general users, this browser is still in use for industrial applications, hence it's worth applying the patch.

What are the relevant tickets?

• 4624

Screenshot (if for frontend)

Checklist

• [x] Added relevant tests or not required
• [x] Didn't break anything

[DennisSuitters]

Excellent, thank you for creating a PR, once I get a moment, I'll test the changes, and if all good do the merge.