Codicon color and URI support to TerminalOptions

[dhuebner]

This is a copy of the original PR #12861
First commit was cherry picked from FernandoAscencio@ba3dda2
In the second commit, I applied the suggested changed from the original PR.

The original description below

What it does

Closes #12074

This commit adds URI and { light, dark } support for terminal icons.
This commit adds ColorTheme support for ThemeIcons
Support for ExtensionTerminalOptions#iconPath

How to test

Open Theia
Install from VSIX the test extension
Check the result follow VSCode test results seen below:

Review checklist

• [ x] As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[tsmaeder]

A couple of initial high-level comments.

[dhuebner]

@tsmaeder
Thanks for your re-view, I will have a look today.

[tsmaeder]

@dhuebner the license check fails. Do we need an ip ticket here?

[dhuebner]

@tsmaeder
It hard to say for me what exactly fails from reading the error log.
The original PR, however, didn't fail #12861
And I added no additional dependencies.

[rschnekenbu]

@dhuebner, there was a message yesterday from Thomas on Theia dev list about those IP checks failing. You may rebase on top of master, that should fix the issue. #13524 is the PR fixing the issue.

[msujew]

@dhuebner @tsmaeder I've updated the PR myself. I've added support for custom icons for quick pick items and quick pick buttons. You can find an example plugin for that here. Simply use the Quick Input Samples command. Use the multiStepInput option to test that the button icons work as expected. With that I was able to align the icon code of terminals and quick picks.