* Add suffix and parameter to trim operator
Fixes#4809
* Unit tests for new trim operator parameters
* Mention trim operator in 5.1.23 release notes
* Address review comments
* Move regex escaping into utils.js trim functions
This way the trimPrefix and trimSuffix functions from utils.js are safe
to call without regex-escaping their parameters, which should make them
easier to use from other parts of the Javascript code.
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