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 :white_check_mark:

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

```diff @@ 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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