Improve diagnostics deduplication (#58220)

tests/cases/compiler/duplicateErrorClassExpression.ts

@@ -0,0 +1,22 @@
+// @strict: true
+
+interface ComplicatedTypeBase {
+    [s: string]: ABase;
+}
+interface ComplicatedTypeDerived {
+    [s: string]: ADerived;
+}
+interface ABase {
+    a: string;
+}
+interface ADerived {
+    b: string;
+}
+class Base {
+    foo!: ComplicatedTypeBase;
+}
+const x = class Derived extends Base {
+    foo!: ComplicatedTypeDerived;
+}
+let obj: { 3: string } = { 3: "three" };
+obj[x];