[JavaScript] (PR provided) End of regex sometimes interpreted as comment

[Thom1729]

Tests:

'// /* /**';
//^^^^^^^^^^ - comment

"// /* /**";
//^^^^^^^^^^ - comment

/test// 1;
// <- string.regexp.js
//    ^ keyword.operator.arithmetic.js

/test/* 1;
// <- string.regexp.js
//    ^ keyword.operator.arithmetic.js
// */

/test/** 1;
// <- string.regexp.js
//    ^^ keyword.operator.arithmetic.js
// */

In the syntax, the comments context is manually included in over twenty places. Presumably, this is a relic of the syntax's heritage as a .tmLanguage, which didn't support prototype contexts. Updating this is a step toward fixing #885, and this bug can be fixed in the process.