Kapt: support incremental compilation in Gradle (KT-13500)

Kapt will process sources on each step of incremental compilation.
(cherry picked from commit 4cb2127)

plugins/annotation-processing/testData/processors/IncrementalDataSimple.kt

@@ -0,0 +1,44 @@
+annotation class Anno
+
+@Anno
+class Test
+
+@Anno
+interface Intf
+
+class Test2 {
+    @Anno
+    fun test2Fun() {}
+}
+
+class Test3 {
+    @Anno
+    class Test3Nested
+    
+    @Anno
+    inner class Test3Inner
+}
+
+class Test4
+
+class Test5 {
+    fun test5Fun() {} 
+}
+
+annotation class Surprise
+
+@Surprise
+class Test6
+
+class Test7 {
+    @Surprise
+    fun test7Fun(): String = "ABC"
+}
+
+class Test8 {
+    @Anno
+    fun test8Fun1() {}
+
+    @Anno
+    fun test8Fun2() {}
+}