Add icon to the tabbar title

[fazibear]

There is a nice icon in terminal tab, but editor tab are without icons. Here is a PR to add them.

Just one question: A margin between an icon and text is a space character at the beginning of the label. Is this done on purpose?

Beautiful codebase BTW ;)

Release Notes:

• Added tabbar title icon

[cla-bot[bot]]

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[fazibear]

@cla-bot check

[cla-bot[bot]]

The cla-bot has been summoned, and re-checked this pull request!

[MatinAniss]

This closed PR seems more complete, https://github.com/zed-industries/zed/pull/12443

[maxdeviant]

Thanks for opening this PR, but I'm going to close this in favor of https://github.com/zed-industries/zed/pull/14523.