FIR Completion: Fix completion in function calls (foo.bar<caret>())

In such expressions, `KtCallExpression` wraps `KtSimpleNameExpression`,
so `getQualifiedExpressionForSelector()` returns `null`

Also, enable tests that are fixed by this

idea/idea-completion/testData/basic/common/AfterIntSeparatedWithComments.kt

@@ -1,3 +1,5 @@
+// FIR_COMPARISON
+
 infix fun Int.func(s: String): Int{}
 
 fun test() {

idea/idea-completion/testData/basic/common/primitiveCompletion/extensionRecompletion.kt

@@ -0,0 +1,13 @@
+// FIR_COMPARISON
+
+class LocalClass
+
+fun LocalClass.ext(action: () -> Unit) {}
+fun LocalClass.extAnother(action: () -> Unit) {}
+
+fun usage(l: LocalClass) {
+    l.ext<caret> {}
+}
+
+// EXIST: ext
+// EXIST: extAnother

idea/idea-completion/testData/basic/common/smartCast/SmartCastAfterIfMethod.kt

@@ -1,3 +1,5 @@
+// FIR_COMPARISON
+
 class Expr {}
 class Num : Expr() {
     fun testing() {}