[1.6.x] Fixed #20852 - Fixed incorrectly generated left quotes in docs.

Sphinx generates left single quotes for apostrophes after
code markup, when right single quotes are required. The
easiest way to fix this is just by inserting the unicode
character for a right single quote.

Instances of the problem were found by looking for
">&#8216;" in the generated HTML.

Backport of c33d1ca1d98003de29cdecb6080b52c5c52139bd from master.