Add matching support for \p{Lc}

This is defined in UAX#44 as being equivalent to
`Lu | Ll | Lt`.

Author: hamishknight

.gitignore

@@ -1,5 +1,8 @@
 .DS_Store
 
+# The current toolchain is dumping files in the package root, rude
+*.emit-module.*
+
 # Xcode
 #
 # gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore

Sources/_StringProcessing/ConsumerInterface.swift

@@ -691,8 +691,9 @@ extension Unicode.ExtendedGeneralCategory {
       ])
 
     case .casedLetter:
-      throw Unsupported(
-        "TODO: cased letter? not the property?")
+      return consumeScalarGCs([
+        .uppercaseLetter, .lowercaseLetter, .titlecaseLetter
+      ])
 
     case .control:
       return consumeScalarGC(.control)

Tests/RegexTests/MatchTests.swift

@@ -693,6 +693,12 @@ extension RegexTests {
     firstMatchTest(#"\p{gc=L}"#, input: "123abcXYZ", match: "a")
     firstMatchTest(#"\p{Lu}"#, input: "123abcXYZ", match: "X")
 
+    // U+0374 GREEK NUMERAL SIGN (Lm)
+    // U+00AA FEMININE ORDINAL INDICATOR (Lo)
+    firstMatchTest(#"\p{L}"#, input: "\u{0374}\u{00AA}123abcXYZ", match: "\u{0374}")
+    firstMatchTest(#"\p{Lc}"#, input: "\u{0374}\u{00AA}123abcXYZ", match: "a")
+    firstMatchTest(#"\p{Lc}"#, input: "\u{0374}\u{00AA}123XYZ", match: "X")
+
     firstMatchTest(
       #"\P{Cc}"#, input: "\n\n\nXYZ", match: "X")
     firstMatchTest(