Add Popover targetElementTag prop

[tgreen7]

Fixes #2250

Checklist

• Enable CircleCI for your fork
• Update documentation

Changes proposed in this pull request:

With the targetElementTag prop passed to Popover or Tooltip you can change the component from a <div> to a <g> (or anything). This makes Tooltips work inside <svg>. The targetComponent prop is passed to react-popper as the component prop.

Reviewers should focus on:

Popover targetElementTag. This should be able to be a string or an JSX.Element see floating-ui/react-popper#107 but I was not sure how to get typescript to allow both.

NEED HELP: adding tests and fixing prop types to allow JSX.Element. As is solves issue #2250

[palantirtech]

Thanks for your interest in palantir/blueprint, @tgreen7! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[giladgray]

@tgreen7 sweet, glad this was easy! please rename for consistency with existing prop.

[giladgray]

rename to targetElementTag to match rootElementTag, and update docs to match the existing prop.

[giladgray]

targetElementTag & docs (see rootElementTag immediately above)

[giladgray]

@tgreen7 per your description notes, i think it's preferable here to not support JSX.Element in this prop (only string) as it covers the SVG use case and we don't have to worry about JSX elements not supporting the DOM props we rely on.

[tgreen7]

@giladgray Thanks, that sounds fine.

[tgreen7]

@giladgray How long do you think it will be before this fix gets into the release?

[giladgray]

@tgreen7 a day or two, will be cutting full 2.0.0 this week

[tgreen7]

@giladgray awesome thanks!