Deprecate extension annotation in favor of Extension

idea/idea-completion/testData/basic/multifile/ExcludedClass/ExcludedClass.dependency.kt

@@ -1,5 +1,5 @@
 package somePackage
 
 class ExcludedClass
-
-class ExtraClass
+// Such strange name here needed to make completion prefix not intersecting with kotlin.Extension
+class ExctraClass

idea/idea-completion/testData/basic/multifile/ExcludedClass/ExcludedClass.kt

@@ -1,4 +1,4 @@
-val x = Ex<caret>
+val x = Exc<caret>
 
 // ABSENT: ExcludedClass
-// EXIST: ExtraClass
+// EXIST: ExctraClass

idea/idea-completion/testData/basic/multifile/ExcludedJavaClass/ExcludedJavaClass.kt

@@ -1,4 +1,4 @@
-val x = Ex<caret>
+val x = Exc<caret>
 
 // ABSENT: ExcludedClass
-// EXIST: ExtraClass
+// EXIST: ExctraClass

idea/idea-completion/testData/basic/multifile/ExcludedJavaClass/somePackage/ExctraClass.java

@@ -0,0 +1,6 @@
+package somePackage;
+
+// Such strange name here needed to make completion prefix not intersecting with kotlin.Extension
+public class ExctraClass {
+
+}

idea/idea-completion/testData/basic/multifile/ExcludedJavaClass/somePackage/ExtraClass.java

@@ -1,5 +0,0 @@
-package somePackage;
-
-public class ExtraClass {
-
-}

idea/idea-completion/testData/basic/multifile/NotImportedExtensionFunction2/NotImportedExtensionFunction2.dependency.kt

@@ -6,7 +6,7 @@ fun (() -> Unit)?.helloFun1() {
 fun Function0<Unit>.helloFun2() {
 }
 
-fun @extension Function1<String, Unit>.helloFun3() {
+fun @Extension Function1<String, Unit>.helloFun3() {
 }
 
 fun Function1<String, Unit>.helloFun4() {

idea/idea-completion/testData/basic/multifile/NotImportedExtensionFunction3/NotImportedExtensionFunction3.dependency.kt

@@ -6,10 +6,10 @@ fun (String.() -> Unit)?.helloFun1() {
 fun Function0<Unit>.helloFun2() {
 }
 
-fun @extension Function1<String, Unit>.helloFun3() {
+fun @Extension Function1<String, Unit>.helloFun3() {
 }
 
-fun @extension Function1<Int, Unit>.helloFun4() {
+fun @Extension Function1<Int, Unit>.helloFun4() {
 }
 
 fun Function1<String, Unit>.helloFun5() {