Add command: Join Lines

[justcla]

IntelliJ command: Smart Line Join
Suggested shortcut: Ctrl+Shift+J

Brings previous line up to current line.
Removes redundant whitespace.

Clever trick: If joining a variable assignment onto code that has just declared the variable, will merge the variable declaration and assignment together (includes removing any redundant variable declaration and removing semi-colon).
This should effectively reverse a "Split variable declaration and assignment" code refactoring.

[justcla]

I have created the JoinLines command and hooked it up to Ctrl+Shift+J.

It just does editorOperations to MoveToEndOfLine, Delete, then DeleteHorizontalWhitespace.

Todo:

• Include it in a single Undo transaction
• Restore the caret to its original location