Redundant curly braces in string template: remove braces for 'this'

#KT-32972 Fixed

idea/idea-core/src/org/jetbrains/kotlin/idea/core/psiModificationUtils.kt

@@ -558,10 +558,14 @@ fun KtModifierList.normalize(): KtModifierList {
 }
 
 fun KtBlockStringTemplateEntry.canDropBraces() =
-    expression is KtNameReferenceExpression && canPlaceAfterSimpleNameEntry(nextSibling)
+    (expression is KtNameReferenceExpression || expression is KtThisExpression) && canPlaceAfterSimpleNameEntry(nextSibling)
 
 fun KtBlockStringTemplateEntry.dropBraces(): KtSimpleNameStringTemplateEntry {
-    val name = (expression as KtNameReferenceExpression).getReferencedNameElement().text
+    val name = if (expression is KtThisExpression) {
+        KtTokens.THIS_KEYWORD.value
+    } else {
+        (expression as KtNameReferenceExpression).getReferencedNameElement().text
+    }
     val newEntry = KtPsiFactory(this).createSimpleNameStringTemplateEntry(name)
     return replaced(newEntry)
 }

idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/necessaryBrackets7.kt

@@ -0,0 +1,2 @@
+// PROBLEM: none
+fun String.bar() = "x <caret>${this.length}"

idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/unnecessaryBrackets9.kt

@@ -0,0 +1,3 @@
+// HIGHLIGHT: GENERIC_ERROR_OR_WARNING
+
+fun String.bar() = "x <caret>${this}"

idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/unnecessaryBrackets9.kt.after

@@ -0,0 +1,3 @@
+// HIGHLIGHT: GENERIC_ERROR_OR_WARNING
+
+fun String.bar() = "x $this"

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -7890,6 +7890,11 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
             runTest("idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/necessaryBrackets6.kt");
         }
 
+        @TestMetadata("necessaryBrackets7.kt")
+        public void testNecessaryBrackets7() throws Exception {
+            runTest("idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/necessaryBrackets7.kt");
+        }
+
         @TestMetadata("unnecessaryBrackets1.kt")
         public void testUnnecessaryBrackets1() throws Exception {
             runTest("idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/unnecessaryBrackets1.kt");
@@ -7929,6 +7934,11 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
         public void testUnnecessaryBrackets8() throws Exception {
             runTest("idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/unnecessaryBrackets8.kt");
         }
+
+        @TestMetadata("unnecessaryBrackets9.kt")
+        public void testUnnecessaryBrackets9() throws Exception {
+            runTest("idea/testData/inspectionsLocal/removeCurlyBracesFromTemplate/unnecessaryBrackets9.kt");
+        }
     }
 
     @TestMetadata("idea/testData/inspectionsLocal/removeEmptyParenthesesFromAnnotationEntry")