Handle the case of completion of class member when member name is being edited

Fixes #17977

src/services/completions.ts

@@ -1195,6 +1195,11 @@ namespace ts.Completions {
                         if (isClassLike(location)) {
                             return location;
                         }
+                        // class c { method() { } b| }
+                        if (isFromClassElementDeclaration(location) &&
+                            (location.parent as ClassElement).name === location) {
+                            return location.parent.parent as ClassLikeDeclaration;
+                        }
                         break;
 
                     default:

tests/cases/fourslash/completionEntryForClassMembers3.ts

@@ -0,0 +1,32 @@
+///<reference path="fourslash.ts" />
+
+////interface IFoo {
+////    bar(): void;
+////}
+////class Foo1 implements IFoo {
+////    zap() { }
+////    /*1*/
+////}
+////class Foo2 implements IFoo {
+////    zap() { }
+////    b/*2*/() { }
+////}
+////class Foo3 implements IFoo {
+////    zap() { }
+////    b/*3*/: any;
+////}
+const allowedKeywordCount = verify.allowedClassElementKeywords.length;
+function verifyHasBar() {
+    verify.completionListContains("bar", "(method) IFoo.bar(): void", /*documentation*/ undefined, "method");
+    verify.completionListContainsClassElementKeywords();
+    verify.completionListCount(allowedKeywordCount + 1);
+}
+
+goTo.marker("1");
+verifyHasBar();
+edit.insert("b");
+verifyHasBar();
+goTo.marker("2");
+verifyHasBar();
+goTo.marker("3");
+verifyHasBar();