When pasting a multiline command with indented blocks, extra indentation
from spaces, or tabs, is generally undesirable, because fish already indents
pipes and blocks. Discard the indentation unless the cursor or the pasted
part is inside quotes.
Users who copied fish_clipboard_paste need to update it because
__fish_commandline_is_singlequoted had an API change and was renamed.
This is to make pasting literals easier.
When a user pastes something, we normally take it as-is.
The exception is when a single-quote is open, e.g. the current token
is
foo'bar
When something is pasted here, we escape single-quotes (`'`) and
backslashes (`\\`), so typing a `'` after it will turn it into a
literal token.
Fixes#967.
