Define primary associated type for RegexComponent.

This defines `RegexComponent<Match>` using the syntax pitched in https://forums.swift.org/t/pitch-2-light-weight-same-type-requirement-syntax/55081.

Author: rxwei

Package.swift

@@ -44,7 +44,8 @@ let package = Package(
             dependencies: ["_MatchingEngine", "_CUnicode"],
             swiftSettings: [
                 .unsafeFlags(["-enable-library-evolution"]),
-                .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"])
+                .unsafeFlags(["-Xfrontend", "-enable-experimental-pairwise-build-block"]),
+                .unsafeFlags(["-Xfrontend", "-enable-parameterized-protocol-types"])
             ]),
         .testTarget(
             name: "RegexTests",

Sources/_StringProcessing/RegexDSL/Core.swift

@@ -11,10 +11,8 @@
 
 import _MatchingEngine
 
-
 /// A type that represents a regular expression.
-public protocol RegexComponent {
-  associatedtype Match
+public protocol RegexComponent<Match> {
   var regex: Regex<Match> { get }
 }
 
@@ -84,9 +82,9 @@ public struct Regex<Match>: RegexComponent {
     self = content.regex
   }
 
-  public init<Content: RegexComponent>(
-    @RegexComponentBuilder _ content: () -> Content
-  ) where Content.Match == Match {
+  public init(
+    @RegexComponentBuilder _ content: () -> some RegexComponent<Match>
+  ) {
     self.init(content())
   }