Handle trivia in code fix forgotten-this

Fixes #21433

src/services/codefixes/fixForgottenThisPropertyAccess.ts

@@ -21,6 +21,8 @@ namespace ts.codefix {
     }
 
     function doChange(changes: textChanges.ChangeTracker, sourceFile: SourceFile, token: Identifier): void {
-        changes.replaceNode(sourceFile, token, createPropertyAccess(createThis(), token));
+        // TODO (https://github.com/Microsoft/TypeScript/issues/21246): use shared helper
+        suppressLeadingAndTrailingTrivia(token);
+        changes.replaceRange(sourceFile, { pos: token.getStart(), end: token.end }, createPropertyAccess(createThis(), token));
     }
 }

tests/cases/fourslash/codeFixForgottenThisPropertyAccess03.ts

@@ -0,0 +1,15 @@
+/// <reference path='fourslash.ts' />
+
+////class C {
+////    foo: number;
+////    constructor() {[|
+////        /* a comment */foo = 10;
+////    |]}
+////}
+
+verify.codeFix({
+    description: "Add 'this.' to unresolved variable",
+    newRangeContent: `
+        /* a comment */this.foo = 10;
+    `
+});