Documentation update for HtmlEscape and HtmlEscapeMode
Documentation update for HtmlEscape and HtmlEscapeMode

Added examples for HtmlEscape and HtmlEscapeMode usage.
Small fixes to texts in file

Closes https://github.com/dart-lang/sdk/pull/47599
https://github.com/dart-lang/sdk/pull/47599

GitOrigin-RevId: c6daa7477982d5a37cfe155780b4f00f8c688748
Change-Id: I82737c8570e31c8e39022c66636282ca776823be
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/218989
Reviewed-by: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Commit-Queue: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk