Add multi-select context menu to experiments webview

[mattseddon]

Now that we have a context menu available in the experiments webview we need to extend it to handle actions on multiple selected rows:

More details and flows in the Figma spec and probably in #1562.

The only action that I can think of that is applicable to a list of selected experiments is "remove" but I could be wrong.

[wolmir]

@maxagin @shcheklein @mattseddon The context menu is disabled when any experiment is running.
Should the row selection be disabled as well?

[mattseddon]

Yes, the same conditions should apply.

[wolmir]

@maxagin

Screen.Recording.2022-06-14.at.16.29.56.mov

[maxagin]

Great work @wolmir ! Tiny comment: When you add the select style you may consider not using the border (top/bottom) at all, as they are moving the other rows :) - unwanted movement.

[maxagin]

I think that if the exp is running I still want to be able to remove it, but just to remove it. WDYT?

[mattseddon]

Discussed on the weekly planning call:

1. Logic in the table should replicate logic shown in the tree (see collectDeletable).
2. Can stop a running experiment which is equivalent to deleting it.

[mattseddon]

We have a multi-select context menu now.