Smart completion for then and else branches of if

#KT-4910 Fixed

idea/testData/completion/smart/IfCondition.kt

@@ -0,0 +1,6 @@
+fun bar(b: Boolean, c: Char){
+    if (<caret>
+}
+
+// EXIST: b
+// ABSENT: c

idea/testData/completion/smart/IfValue1.kt

@@ -0,0 +1,10 @@
+fun foo(s: String){}
+fun foo(c: Char){}
+
+fun bar(b: Boolean, s: String, c: Char){
+    foo(if (b) <caret>)
+}
+
+// EXIST: s
+// EXIST: c
+// ABSENT: b

idea/testData/completion/smart/IfValue2.kt

@@ -0,0 +1,10 @@
+fun foo(s: String){}
+fun foo(c: Char){}
+
+fun bar(b: Boolean, s: String, c: Char){
+    foo(if (b) "abc" else <caret>)
+}
+
+// EXIST: s
+// ABSENT: c
+// ABSENT: b

idea/testData/completion/smart/IfValue3.kt

@@ -0,0 +1,10 @@
+fun foo(s: String){}
+fun foo(c: Char){}
+
+fun bar(b: Boolean, s: String, c: Char){
+    foo(if (b) xxx else <caret>)
+}
+
+// EXIST: s
+// EXIST: c
+// ABSENT: b