New enum syntax: Short constructor syntax introduced for entries, optional commas between entries, semicolon after entries. #KT-7605 Fixed.

Grammar changed accordingly.
Semicolons prohibited after an entry except the last one.
Only one initializer is allowed per entry.
EnumReferenceExpression AST node introduced.
Some tests fixed, a pair of new tests written. Kotlin code inside project fixed.
Formatter and intendation tests fixed accordingly.
Stub version is incremented.

compiler/testData/psi/EnumCommas.kt

@@ -0,0 +1,7 @@
+enum class Color {
+    NORTH,
+    SOUTH,
+    WEST,
+    EAST,
+    ;
+}