refactor: add in a Rewrites.applyAction helper

This also has a small change where instead of applying all the actions
if we are doing a rewrite, we only actually take the first one

[Cherry-picked e97fea5]

compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala

@@ -11,6 +11,7 @@ import dotty.tools.dotc.util.SourcePosition;
 
 import java.io.OutputStreamWriter
 import java.nio.charset.StandardCharsets.UTF_8
+import dotty.tools.dotc.reporting.CodeAction
 
 /** Handles rewriting of Scala2 files to Dotty */
 object Rewrites {
@@ -99,6 +100,14 @@ object Rewrites {
       report.echo(s"[patched file ${source.file.path}]")
       rewrites.patched(source).writeBack()
     }
+
+  /** Given a CodeAction take the patches and apply them.
+   *
+   * @param action The CodeAction containing the patches
+   */
+  def applyAction(action: CodeAction)(using Context): Unit =
+    action.patches.foreach: actionPatch =>
+      patch(actionPatch.srcPos.span, actionPatch.replacement)
 }
 
 /** A completely encapsulated class representing rewrite state, used

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -54,6 +54,7 @@ import cc.CheckCaptures
 import config.Config
 
 import scala.annotation.constructorOnly
+import dotty.tools.dotc.rewrites.Rewrites
 
 object Typer {
 
@@ -2882,8 +2883,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         if (migrateTo3) {
           // Under -rewrite, patch `x _` to `(() => x)`
           msg.actions
-            .flatMap(_.patches)
-            .map(actionPatch => patch(actionPatch.srcPos.span, actionPatch.replacement))
+            .headOption
+            .foreach(Rewrites.applyAction)
           return typed(untpd.Function(Nil, qual), pt)
         }
     }
@@ -3887,8 +3888,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         || Feature.warnOnMigration(msg, tree.srcPos, version = `3.0`)
           && { 
             msg.actions
-              .flatMap(_.patches)
-              .map(actionPatch => patch(actionPatch.srcPos.span, actionPatch.replacement))
+              .headOption
+              .foreach(Rewrites.applyAction)
             true
           }