Upgrade fontawesome version to latest (v6) from v5 Resolves #2242

[SPWwj]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:
Resolves #2242
Upgrade from fontawesome-free@5.15.4 to fontawesome-free@6.4.0.
The current icons will be preserved. In addition, this PR allows the use of FontAwesome v6 icons
For detail refer to backward-compatibility
Code:

:fa-solid-house:
:far-file-code:
:fa-brands-facebook:
:fab-facebook:

Output:

Anything you'd like to highlight/discuss:
V6 has moved regular icons to the pro version.
However, the free icons in v5 should still be usable due to backward compatibility.
Thus user does not need to do anything and no cost in keeping current icons.

The fas and fab icons have been renamed to fa-solid and fa-brands, respectively.

Testing instructions:

Create a new project and try out the instructions provided in the Markbind Icon documentation,
with new v6 icons

Proposed commit message: (wrap lines at 72 characters)
Upgrade font awesome version to latest (v6) from v5

---

Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

Migration Guide

We upgraded from fontawesome-free@5.15.4 to fontawesome-free@6.4.0.
The current icons will be preserved (i.e. you don't have to make any changes if you don't want to) due to Font Awesome's backward compatibility.
With Version 6

• new icons are available
• some icons have been renamed
• syntax/usage has changed slightly

For details please refer to Font Awesome's changelog

[damithc]

The current icons will be preserved. In addition, this PR allows the use of FontAwesome v6 icons

@SPWwj This is great. In fact, this reduces the need for this to be included in V5 major release, as it will no longer be a breaking change.

[tlylt]

Thanks @SPWwj, some nits. Also, could you fill in the PR description to aid PR review?
Specifically:

• any problem encountered during the migration? any things to note for this migration?
• how to test your change
• from users' POV: what update do they need and what new icons are now available?
• what is the cost of keeping the current icons, if any?
• etc

[SPWwj]

Thanks @SPWwj, some nits. Also, could you fill in the PR description to aid PR review? Specifically:

• any problem encountered during the migration? any things to note for this migration?
• how to test your change
• from users' POV: what update do they need and what new icons are now available?
• what is the cost of keeping the current icons, if any?
• etc

PR description updated. There should be no impact from the users' POV based on FontAwesome's backward-compatibility.

[tlylt]

Thanks @SPWwj, some nits. Also, could you fill in the PR description to aid PR review? Specifically:

• any problem encountered during the migration? any things to note for this migration?
• how to test your change
• from users' POV: what update do they need and what new icons are now available?
• what is the cost of keeping the current icons, if any?
• etc

PR description updated. There should be no impact from the users' POV based on FontAwesome's backward-compatibility.

Please fill in the proposed commit message as well. Yes I agree that from users' POV there's no change, but I think we should gently mention the differences brought about in this version upgrade (e,g, how it's still backward-compatible, but we may not be able to guarantee that in the future).

Will be helping out on this.

[tlylt]

LGTM, thank you @SPWwj 🚀

[tlylt]

@all-contributors please add @SPWwj for doc, code

[allcontributors]

@tlylt

I've put up a pull request to add @SPWwj! 🎉