Deprecate extension annotation in favor of Extension

idea/testData/decompiler/decompiledText/FunctionTypes/FunctionTypes.kt

@@ -21,9 +21,9 @@ class FunctionTypes {
     public fun f2(f: Function2<Int, *, String>) {
     }
 
-    public fun f3(f: @extension Function2<Int, Int, Unit>) {
+    public fun f3(f: @Extension Function2<Int, Int, Unit>) {
     }
 
-    public fun f4(f: List<@extension Function1<*, *>>) {
+    public fun f4(f: List<@Extension Function1<*, *>>) {
     }
 }

idea/testData/decompiler/stubBuilder/Types/Types.kt

@@ -19,7 +19,7 @@ abstract class Types {
 
     abstract val starList: List<*>
     abstract val starFun: Function1<*, *>
-    abstract val extFun: @extension Function2<Int, Int, Unit>
-    abstract val listExtStarFun: List<@extension Function1<*, *>>
+    abstract val extFun: @Extension Function2<Int, Int, Unit>
+    abstract val listExtStarFun: List<@Extension Function1<*, *>>
     abstract val funTypeWithStarAndNonStar: Function1<*, Int>
 }