Make 'Find All in single file' more discoverable

[peterflynn]

Spinning this off as a bug-sized chunk from the Find/Replace epic research.

Currently, it's possible get the Find All panel's bulk results listing for a single file by right-clicking that file and choosing "Find in..." -- but this isn't discoverable for some users.

Possible solutions:

• Add "Find all in current file" or somesuch to menu next to existing Find, Find All commands. (This would be more palatable if we forked off a new Search top-level menu, as suggested in [UX] Move Find items to different menu? #6084).
• Add a button in the Find toolbar to switch the current search into Find All (in file) mode. (Some other editors have a gesture like this).

[marcelgerber]

I like the second idea better (a Search menu would also be cool, but we needn't put to much things in). Maybe something like this?

If you like this one, I could try to work on it.

[lkcampbell]

@peterflynn, your first suggestion should be addressed with the PR I just submitted: #7488.

It adds a new "File in Selected File/Folder" menu item to the new Search menu.