Fix edge cases on jsx-pascal-case

[yacinehmito]

Currently the rule jsx-pascal-case doesn't support some edge cases:

• It improperly errors when the component is in a namespace that starts with an underscore
• It improperly succeeds on the component is in camelCase
• It improperly succeeds in a bunch of cases where the component is in a namespace
• It doesn't accurately report the name of the component in some error cases

The PR should fix #1334

[yacinehmito]

There is no fix yet. I am waiting for #2636 to be merged.
For the moment the PR only adds new test cases.

[yacinehmito]

The PR #2638 is now sufficient to fix #1334.

Keeping this one around though to make sure that jsx-pascal-case doesn't trigger an error when a colon is used in a tag.

[yacinehmito]

Fixed the test cases after having worked on #2638.
This showcases that #1334 is not truly fixed yet.

I'll work on it after #2636 and #2640 are sorted out.

[ljharb]

@yacinehmito are you interested in completing this PR?

[yacinehmito]

I am sorry, I lost interest as I was not using React anymore.

[ljharb]

@yacinehmito i'd still prefer to leave it open so someone else can finish it, if that's ok :-)