Scala should support Unicode supplementary characters

[scabug]

Currently the parser only understands identifiers drawn from the basic multilingual plane.

See https://www.oracle.com/technical-resources/articles/javase/supplementary.html for more information on how we would support this on the Java target.

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Imported From: https://issues.scala-lang.org/browse/SI-1406?orig=1
Reporter: Geoffrey Alan Washburn (washburn)

[magnolia-k]

The Scala compiler uses Character.isUnicodeIdentifierPart to determine which Unicode characters can be used as identifiers. There are two versions of this function, one that takes char type as an argument and one that takes int type as an argument.

The current Scala compiler uses a function that takes char type as an argument, so it is unable to correctly determine Unicode supplementary characters.

Character.isHighSurrogate needs to be called character by character to check if the character is a high surrogate or not.