Deprecate extension annotation in favor of Extension

idea/testData/unifier/equivalence/types/function0.kt

@@ -4,4 +4,4 @@ val c: <selection>() -> String</selection> = { "" }
 val d: () -> kotlin.String = { "" }
 val e: () -> Unit = {  }
 val f: Any.() -> String = { "" }
-val g: @extension Function1<String, String> = { "" }
+val g: @Extension Function1<String, String> = { "" }

idea/testData/unifier/equivalence/types/function1.kt

@@ -5,6 +5,6 @@ val d: (n: Int) -> kotlin.String = { "" }
 val e: (String) -> Int = { 0 }
 val f: () -> Int = { 0 }
 val g: Int.() -> String = { "" }
-val h: @extension Function2<Int, Int, String> = { "" }
+val h: @Extension Function2<Int, Int, String> = { "" }
 val i: (m: Int) -> kotlin.String = { "" }
-val j: @extension Function1<Int, String> = { "" }
+val j: @Extension Function1<Int, String> = { "" }

idea/testData/unifier/equivalence/types/function1.kt.match

@@ -10,4 +10,4 @@ Int.() -> String
 
 (m: Int) -> kotlin.String
 
-@extension Function1<Int, String>
+@Extension Function1<Int, String>

idea/testData/unifier/equivalence/types/function2.kt

@@ -6,6 +6,6 @@ val e: (String) -> Int = { 0 }
 val f: () -> Int = { 0 }
 val g: Any.(Int) -> String = { "" }
 val h: Int.(Any) -> String = { "" }
-val i: @extension Function3<Any, Any, Int, String> = { a, b -> "" }
+val i: @Extension Function3<Any, Any, Int, String> = { a, b -> "" }
 val j: (t: Any, u: Int) -> kotlin.String = { a, b ->  "" }
-val k: @extension Function2<Any, Int, String> = { "" }
+val k: @Extension Function2<Any, Int, String> = { "" }

idea/testData/unifier/equivalence/types/function2.kt.match

@@ -10,4 +10,4 @@ Any.(Int) -> String
 
 (t: Any, u: Int) -> kotlin.String
 
-@extension Function2<Any, Int, String>
+@Extension Function2<Any, Int, String>