Fix: make RTL new line a valid character

[whazor]

Issue #, if available: #5423

Description of changes:
We create a mechanism for specifying valid control characters. In this way, we can set wished behaviors, without making RTL mode less secure.

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 87.58%. Comparing base (142b607) to head (9692cce).
Report is 136 commits behind head on master.

Files with missing lines	Patch %	Lines
src/layer/text.js	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5434      +/-   ##
==========================================
- Coverage   87.59%   87.58%   -0.01%     
==========================================
  Files         584      584              
  Lines       46408    46411       +3     
  Branches     7021     7021              
==========================================
+ Hits        40650    40651       +1     
- Misses       5758     5760       +2     

Flag	Coverage Δ
unittests	87.58% <50.00%> (-0.01%)	⬇️

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[akoreman]

Should we add a test covering this new behaviour?

[nightwing]

Would it be better to just skip the first character if it is rtl mark and keep 5he old code for the rest?