docs: add Edge to flexbox supported browsers

[ncoden]

Description

Added Edge to flexbox supported browsers (info from caniuse.com) and small SPaG fix

Opened from #11239 (@danielrhodeswarp). I rebased commits and added the requested changes.

Motivation and Context

Completes the info and fixes a SPaG issue

Screenshots (if appropriate):

Types of changes

• Documentation
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to change)

Checklist (all required):

• I have read and follow the CONTRIBUTING document.
• There are no other pull request similar to this one.
• The pull request title is descriptive.
• The template is fully and correctly filled.
• The pull request targets the right branch (develop or support/*).
• My commits are correctly titled and contain all relevant information.
• My code follows the code style of this project.
• I have updated the documentation accordingly to my changes (if relevant).
• I have added tests to cover my changes (if relevant).
• All new and existing tests passed.

[ncoden]

Poke @DanielRuf for review :)

Yeah, this PR is really simply but at least one review is required to merge!