Markdown: Treat CJK punctuation symbols as letters

Some aspects of the commonmark spec do not play well with CJK languages.

For example, according to the spec punctuation should be handled as whitespaces hence
a**.test.**b should NOT be bold, whereas a**test**b has test in bold.

This is problematic for Chinese users. This FR is used to track a proposed deviation from the commonmark spec: handle Chinese punctuation symbols (that are different from regular punctuation symbols) as regular letters.


Add a use case.

**啦。**啦 cannot be parsed properly in live preview:

The reader mode does not have this issue: