email.xml: Detect nested comments and escaped characters

Merged Martin Walch requested to merge martinwalch/syntax-highlighting:bug425345 into master

Conform to RFC 822 and 5322:

  • Add support for nested comments.
  • Add support for escaped characters in comments.
  • Extend support for escaped characters in quoted strings.
  • Extend and update test cases accordingly.

BUG: 425345
FIXED-IN: 5.79.0

Edited by Martin Walch

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