Formalize Unicode block properties

Previously we only supported a subset of the
Oniguruma spellings for these. Introduce them as
an actual Unicode property with the key `blk` or
`block`.

Additionally, allow a non-Unicode shorthand syntax
that uses the prefix `in`. This is supported by
Oniguruma and Perl (though Perl discourages its
usage). We may want to warn/error on it and suggest
users switch to the more explicit form.

Author: hamishknight

Sources/_RegexParser/Regex/AST/Atom.swift

@@ -441,13 +441,15 @@ extension AST.Atom.CharacterProperty {
 
     /// Character age, as per UnicodeScalar.Properties.age.
     case age(major: Int, minor: Int)
-    
+
+    /// A block property.
+    case block(Unicode.Block)
+
     case posix(Unicode.POSIXProperty)
 
     /// Some special properties implemented by PCRE and Oniguruma.
     case pcreSpecial(PCRESpecialCategory)
-    case onigurumaSpecial(OnigurumaSpecialProperty)
-    
+
     public enum MapKind: Hashable {
       case lowercase
       case uppercase

Sources/_RegexParser/Regex/Parse/CharacterPropertyClassification.swift

@@ -62,6 +62,7 @@ enum ParseError: Error, Hashable {
   case unknownProperty(key: String?, value: String)
   case unrecognizedScript(String)
   case unrecognizedCategory(String)
+  case unrecognizedBlock(String)
   case invalidAge(String)
   case invalidNumericValue(String)
   case unrecognizedNumericType(String)
@@ -195,6 +196,8 @@ extension ParseError: CustomStringConvertible {
       return "unrecognized script '\(value)'"
     case .unrecognizedCategory(let value):
       return "unrecognized category '\(value)'"
+    case .unrecognizedBlock(let value):
+      return "unrecognized block '\(value)'"
     case .unrecognizedNumericType(let value):
       return "unrecognized numeric type '\(value)'"
     case .invalidAge(let value):

Sources/_RegexParser/Regex/Parse/Diagnostics.swift

@@ -173,7 +173,7 @@ extension RegexValidator {
       break
     case .pcreSpecial:
       throw error(.unsupported("PCRE property"), at: loc)
-    case .onigurumaSpecial:
+    case .block:
       throw error(.unsupported("Unicode block property"), at: loc)
     }
   }