Detect invalid escape for ecmascript

[justin-tay]

This fixes the test failure from the JSON Schema Test Suite in optional/ecmascript-regex.json as joni does not detect invalid escapes.

This makes the following changes

• The regex format has been changed to also follow the configuration of whether to use ecma-262 compliant regex. Previously it always used the jdk regex.
• The JoniRegularExpression implementation uses a regex to detect if an invalid escape is used as joni doesn't detect invalid escapes. In actuality it's upstream Oniguruma doesn't actually support ecma as a syntax.
• The latest tests from the JSON Schema Test Suite for optional/ecmascript-regex.json has been updated. In actuality it doesn't change anything but it is clearer that "format": "regex" is used in the test
• The test harness now enables format assertions when running the optional/ecmascript-regex.json test

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.74%. Comparing base (48ca3c2) to head (e11488a).
Report is 19 commits behind head on master.

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1049      +/-   ##
============================================
- Coverage     78.90%   78.74%   -0.16%     
- Complexity     1965     2033      +68     
============================================
  Files           172      191      +19     
  Lines          6352     6596     +244     
  Branches       1255     1260       +5     
============================================
+ Hits           5012     5194     +182     
- Misses          867      927      +60     
- Partials        473      475       +2     

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