Add editor: convert to sentence case (#35015)

This PR adds an `editor: convert to sentence case` action.

I frequently find myself copying branch names and then removing the
hyphens and ensuring the first letter is capitalized, and then using the
result text for the commit message.

For example:

<img width="927" height="482" alt="image"
src="https://github.com/user-attachments/assets/adf14a37-a92e-44df-8c0e-267b5c7677fb"
/>

You can achieve this with a combination of other text manipulation
commands, but this action makes it even easier.

Also, moved `toggle_case` down into the area where all other commands
internally using `manipulate_text` are located.

Release Notes:

- Added `editor: convert to sentence case`

crates/editor/src/actions.rs

@@ -365,6 +365,8 @@ actions!(
         ConvertToLowerCase,
         /// Toggles the case of selected text.
         ConvertToOppositeCase,
+        /// Converts selected text to sentence case.
+        ConvertToSentenceCase,
         /// Converts selected text to snake_case.
         ConvertToSnakeCase,
         /// Converts selected text to Title Case.