Treat {{!}} as a magic word

 * Builds on c4f3a2be5e8893aa8df9ee445438b07426d9406e.

 * Fixes the tests from d51e64097bb1b18e356584d4f3ddcfd90a6071ba.

 * Surfaced a bug in the TokenStreamPatcher where converting to string
   should actually be reprocessing the line in non-sol context. Master
   currently fails on examples like:

     | say ''foo''' | bar ''' baz ''

   This will be investigated in a follow up patch and may require moving
   the TokenStreamPatcher to an async phase in the pipeline. TBD.

Bug: 67863
Change-Id: I9de0844a06c7cf621940c9f2b41c91eb3c9692e1