complete for functions creating React.element when in a JSX context

[zth]

Something I've wanted for a while. This will add React.string, React.array etc to the completion items for relevant types in pipe when in a JSX context. Being in a JSX context is defined as a) being in the body of a make function annotated with @react.component, or b) being inside of JSX.

Example:
Doing pipe completion on an int in JSX context will return React.int in the completion items, in addition to the builtin completions for int.

This accomplishes two things:

1. Convenience, since you otherwise have to first complete for React, and then the fn you're after.
2. Helps beginners with understanding that you in ReScript need to use the respective React.element producing functions in JSX.

[cristianoc]

Restoring context seems wrong.

[cristianoc]

Go ahead merge after fixing the code for restoring the context.