Process '$' correctly in "Convert concatenation to template"

So #KT-12226 Fixed

idea/testData/intentions/convertToStringTemplate/dollarSignChar.kt

@@ -0,0 +1,3 @@
+fun test(): String {
+    return "" + '$' + "foo" + '$' + "bar" + '$'<caret>
+}

idea/testData/intentions/convertToStringTemplate/dollarSignChar.kt.after

@@ -0,0 +1,3 @@
+fun test(): String {
+    return "\$foo\$bar$"<caret>
+}