Fix completion for back-ticked name (KT-19863, KT-19864)

^KT-19863 Fixed
^KT-19864 Fixed

idea/idea-completion/testData/handlers/basic/KT19863.kt

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked`() {}
+
+fun test() {
+    `ba<caret>
+}
+
+// ELEMENT: backticked

idea/idea-completion/testData/handlers/basic/KT19863.kt.after

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked`() {}
+
+fun test() {
+    backticked()<caret>
+}
+
+// ELEMENT: backticked

idea/idea-completion/testData/handlers/basic/KT19864.kt

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked~name`() {}
+
+fun test() {
+    `ba<caret>
+}
+
+// ELEMENT: backticked~name

idea/idea-completion/testData/handlers/basic/KT19864.kt.after

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked~name`() {}
+
+fun test() {
+    `backticked~name`()<caret>
+}
+
+// ELEMENT: backticked~name