Cleanup rules for Thai

[bact]

• remove
  • periods and spaces at the beginning and end of sentence
  • orphan period
  • zero-width chars (occurs in some Thai texts, due to input method or some processing)
• add
  • a space before and after Maiyamok, ?, and !
• condense
  • repetitive chars to one char: spaces, Maiyamok
• normalize
  • Sara E + Sara E -> Sara Ae
  • Nikhahit + (Tone marks +) Sara Aa -> (Tone marks +) Sara Am

--

See guidelines from the Office of the Royal Society

• , comma http://www.royin.go.th/?page_id=10392 (in bibliography/index use case, removing comma may change the sentence's semantic, but that use case seems irrelevant here and in any case does not affect sound)
• : colon http://www.royin.go.th/?page_id=10399
• ? question mark http://www.royin.go.th/?page_id=10418
• ! exclamation mark http://www.royin.go.th/?page_id=10433
• ๆ Maiyamok http://www.royin.go.th/?page_id=10427

See also validation rules #318

[bact]

Discourse discussion
https://discourse.mozilla.org/t/thai-th-rules-for-validation-and-cleanup-for-discussion/66703