Add hasMatch, firstMatch, and stringMatch to Pattern, String

[munificent]

Both String and RegExp implement Pattern, which is awesome. You can generically treat a String as if it were a RegExp... except that Pattern doesn't have all of the methods that RegExp provides. Pattern mysteriously leaves off hasMatch, firstMatch, and stringMatch, which means String also lacks them.

[lrhn]

Removed Type-Defect label. Added Type-Enhancement label.

[alan-knight]

Ran into this today. It would be nice to be able to, say, find the .dart files in a list of arguments.    args.where((each) => '.dart'.hasMatch(each)) The alternatives are both more awkward to write and less efficient.

[lrhn]

The problem is that adding more methods to Pattern also means adding them to String, and the name generally don't look as fitting on a String as on a more specialized pattern.

The solution is usually to use the "reverse method" on String:   args.where((each) => each.contains(".dart")); // or even .endsWith(...)

Methods on Pattern/RegExp often exists to support methods on String, so there is usually a corresponding method on string that takes a Pattern which should not be awkward (if it is, do speak up!)

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Added NotPlanned label.