JSX/TSX: Tags of React components are styled as classes

[RunDevelopment]

This PR implements #1518 but it uses class-name in favor of the proposed tag-class. Like this, we don't have to change the themes.

The PR adds a class-name alias to all the tags of React components. Tags which start with an uppercase letter are considered React components.
HTML tags remain unchanged.

The new styling is similar to VS Code's.

Example: (taken from the React tutorial)

VS Code:

[mAAdhaTTah]

Hey @RunDevelopment – Just wanted to say I appreciate the reviews & PRs you've made to Prism. I haven't had a lot of time to dig into all of them, and a lot of the regex changes I'm unfortunately not really qualified to review, but I just wanted to let you know we see the work you've done and thank you for it.

[Templarian]

@RunDevelopment Thanks for writing this so quickly, exactly what I needed. The code/results looks good to me. 😃

[atomiks]

Could this be changed to tag-component or tag-class instead of class-name. The reason is to desire as much granularity with the highlighting as possible, if we don't want the JavaScript class color to match the component tag color.

[Templarian]

@atomiks The theme will just use a more specific CSS selector.

.token.tag.class-name {
    color: red;
}

[atomiks]

Ah ok, looks good then!

[mAAdhaTTah]

Can we get tests for this?

[RunDevelopment]

Unfortunately, it is not possible to test this feature with our usual tests.
Because this PR only adds an alias to a token, the alias will not show up in the JSON (see jsx/tag_feature.test which I did not have to change, but is styled like a class in the test page.).

[mAAdhaTTah]

But you could confirm that <Button /> styles Button as a class-name?

[RunDevelopment]

But you could confirm that styles Button as a class-name?

Depends:
With the current implementation of this PR and the test suite, definitely no.

But, we could change the implementation of this PR so that it will replace the string Button with a new token with the type class-name. instead of adding an alias to the tag token. That will be testable.

[mAAdhaTTah]

I dig this, much closer to what I was thinking.

[RunDevelopment]

One last note:

Because the implementation is now different, the CSS selector to highlight the class-name token of tags has to look like this:

.token.tag > .token.class-name {
    color: red;
}