Fix: escape when input to FilterInput is one double quote

Created by: attfarhan

Fixes https://github.com/sourcegraph/sourcegraph/issues/8418.

Now we'll just detect if the user has typed in " as the input, and escape it if so. I'm not sure this is the correct solution, it seems like the content field has trouble with quotes more generally. cc @rvantonder as described in https://github.com/sourcegraph/sourcegraph/issues/8418#issuecomment-603633755