fix KotlinAndroidAddStringResource: correct generic extension function processing + minor refactoring

idea/testData/android/resourceIntentions/kotlinAndroidAddStringResource/genericContextExtensionFunction/expected/main.kt

@@ -0,0 +1,5 @@
+package com.myapp
+
+import android.content.Context
+
+fun <T: Context> T.getText(): String? = getString(R.string.resource_id)

idea/testData/android/resourceIntentions/kotlinAndroidAddStringResource/genericContextExtensionFunction/expected/res/values/strings.xml

@@ -0,0 +1,3 @@
+<resources>
+    <string name="resource_id">some text</string>
+</resources>

idea/testData/android/resourceIntentions/kotlinAndroidAddStringResource/genericContextExtensionFunction/genericContextExtensionFunction.test

@@ -0,0 +1,5 @@
+{
+  "rFile": "../../R.kt",
+  "resDirectory": "../../res",
+  "intentionClass": "org.jetbrains.kotlin.android.intentions.KotlinAndroidAddStringResource"
+}

idea/testData/android/resourceIntentions/kotlinAndroidAddStringResource/genericContextExtensionFunction/main.kt

@@ -0,0 +1,5 @@
+package com.myapp
+
+import android.content.Context
+
+fun <T: Context> T.getText(): String? = "some <caret>text"