Completion: add root prefix support

#KT-10340 Fixed

idea/idea-completion/testData/handlers/basic/ClassNameForMethodWithPackageConflict.kt

@@ -0,0 +1,9 @@
+// WITH_RUNTIME
+
+fun buildTemplates() {
+    val kotlin = 42
+    printl<caret>
+}
+
+// ELEMENT: println
+// TAIL_TEXT: "() (kotlin.io)"

idea/idea-completion/testData/handlers/basic/ClassNameForMethodWithPackageConflict.kt.after

@@ -0,0 +1,9 @@
+// WITH_RUNTIME
+
+fun buildTemplates() {
+    val kotlin = 42
+    println()<caret>
+}
+
+// ELEMENT: println
+// TAIL_TEXT: "() (kotlin.io)"

idea/idea-completion/testData/handlers/basic/ClassNameForMethodWithPackageConflict2.kt

@@ -0,0 +1,8 @@
+// WITH_RUNTIME
+class kotlin
+fun buildTemplates() {
+    printl<caret>
+}
+
+// ELEMENT: println
+// TAIL_TEXT: "() (kotlin.io)"

idea/idea-completion/testData/handlers/basic/ClassNameForMethodWithPackageConflict2.kt.after

@@ -0,0 +1,8 @@
+// WITH_RUNTIME
+class kotlin
+fun buildTemplates() {
+    println()<caret>
+}
+
+// ELEMENT: println
+// TAIL_TEXT: "() (kotlin.io)"

idea/idea-completion/testData/handlers/basic/ClassNameWithPackageConflict.kt

@@ -0,0 +1,7 @@
+fun buildTemplates() {
+    val java = 1123
+    Coll<caret>
+}
+
+// ELEMENT: Collections
+// TAIL_TEXT: " (java.util)"

idea/idea-completion/testData/handlers/basic/ClassNameWithPackageConflict.kt.after

@@ -0,0 +1,9 @@
+import java.util.Collections
+
+fun buildTemplates() {
+    val java = 1123
+    Collections<caret>
+}
+
+// ELEMENT: Collections
+// TAIL_TEXT: " (java.util)"

idea/idea-completion/testData/handlers/basic/StaticFunctionFromJavaWithConflict.kt

@@ -0,0 +1,7 @@
+fun buildTemplates() {
+    val java = 42
+    Arrays.bina<caret>
+}
+
+// ELEMENT: binarySearch
+// TAIL_TEXT: "(a: IntArray!, key: Int) (java.util)"

idea/idea-completion/testData/handlers/basic/StaticFunctionFromJavaWithConflict.kt.after

@@ -0,0 +1,9 @@
+import java.util.Arrays
+
+fun buildTemplates() {
+    val java = 42
+    Arrays.binarySearch()
+}
+
+// ELEMENT: binarySearch
+// TAIL_TEXT: "(a: IntArray!, key: Int) (java.util)"