Koenig - Improve MD text expansion behaviour
Koenig - Improve MD text expansion behaviour

refs https://github.com/TryGhost/Ghost/issues/9505
- fix overzealous matching of inline formatting
  - ensure the match starts with a space or the start of the paragraph
  - ensure the start matched chars are not followed by a space
  - ensure the end matched chars are not preceded by a space
  - avoid matching more MD chars than expected
- allow text expansions to work when editing text in the middle of a paragraph
  - do not add a trailing space after reformatting in this case

kevinansfield/Ghost-Admin,TryGhost/Ghost-Admin,kevinansfield/Ghost-Admin,acburdine/Ghost-Admin,acburdine/Ghost-Admin,TryGhost/Ghost-Admin