Fix: Correctly support empty type parameters

[j-f1]

This makes the parser handle the let a: Foo<> case properly.

Unfortunately, the change seems to cause a regression in one test due to a bug in the TypeScript parser. Any ideas about why this happens would be appreciated.

[eslintbot]

Thanks for the pull request, @j-f1! I took a look to make sure it's ready for merging and found some changes are needed:

• Pull requests with code require an issue to be mentioned at the end of the commit summary, such as (fixes #1234). Please update the commit summary with an issue (file a new issue if one doesn't already exist).

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[JamesHenry]

Thanks so much for your patience on this @j-f1! You both highlighted a fundamental issue in the way we were handling that and got the ball rolling on a fix. Your contributions of the last few months to both the parser and the plugin have been very valuable, so thank you!

I created an issue for it, and included the minimal possible test case from yours as part of the overall fix which matches up with babylon's output: #396

I do not make a habit of closing people's PRs in favour of my own, but I am super keen to push on with my greatly improved availability for open source this week, so that is the route I am going to take on this occassion.

Thank you once again!