Fix text transformation commands for multiple line, single selection cases

[JosephTLyons]

If you highlight the following block of text (with a single selection):

The quick brown
fox jumps over
the lazy dog

and run editor: convert to upper camel case, you'll get:

TheQuickBrown
foxJumpsOver
theLazyDog

instead of:

TheQuickBrown
FoxJumpsOver
TheLazyDog

The same thing happens for editor: convert to title case. This happens because to_case crate doesn't allow the user to define '\n' as a boundary. I wanted to fix this at the lib level, so I filled an issue but I never heard back. What's strange is VS Code and Sublime I think both exhibit the same output as we do currently, but I don't personally think this feels right (happy to hear opposing opinions). I'm just doing the naive thing to hack around this limitation of the to_case crate.

I did some testing and it seems I only need to adjust editor: convert to title case and editor: convert to upper camel case. The way the other transformations are implemented in to_case don't seem to have this issue.

Release Notes:

• Fixed a bug where running certain text transfomration commands on a single selection covering multiple lines would not transform all selected lines as expected.