:lipstick: Deprecate backspaceToBeginningOf{Word,Line}

Rename functions:
`Editor::backspaceToBeginningOfWord` => `Editor::deleteToBeginningOfWord`
`Editor::backspaceToBeginningOfLine` => `Editor::deleteToBeginningOfLine`
`Selection::backspaceToBeginningOfWord` => `Selection::deleteToBeginningOfWord`
`Selection::backspaceToBeginningOfLine` => `Selection::deleteToBeginningOfLine`

Rename commands:
`editor:backspace-to-beginning-of-word` => `editor:delete-to-beginning-of-word`
`editor:backspace-to-beginning-of-line` => `editor:delete-to-beginning-of-line`

Fix #1791

/cc @probablycorey