Support for unicode primes on identifiers.

GHC should allow the (single/double/triple/quadruple) prime characters in Unicode to be allowed in identifiers. This would make them consistent with the ASCII apostrophe, which is usually used in place of a single prime. The current workaround for primes (using one or more apostrophes) is unwieldy for higher primes (e.g. a''' and a'''').

All of the following identifiers should be valid.

a'   // U+0027 APOSTROPHE
a′   // U+2032 PRIME
a″   // U+2033 DOUBLE PRIME
a‴   // U+2034 TRIPLE PRIME
a⁗   // U+2057 QUADRUPLE PRIME

Trac metadata

Trac field	Value
Version	7.10.2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler (Parser)
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