Improve AddInitKeyword quickfix

- Extract quickfix method
- Delete redundant semicolon
- Do not replace initializer PSI element

idea/testData/quickfix/modifiers/beforeAddInitKeywordRemoveSemicolonSameLine.kt

@@ -0,0 +1,8 @@
+// "Add 'init' keyword" "true"
+fun foo() = 1
+class A {
+    val prop = foo()
+    ;<caret>{
+
+    }
+}