fix(47256): show deprecated on index signatures (microsoft#47400)

Author: a-tarasyuk

src/compiler/checker.ts

@@ -28587,6 +28587,9 @@ namespace ts {
                 if (compilerOptions.noPropertyAccessFromIndexSignature && isPropertyAccessExpression(node)) {
                     error(right, Diagnostics.Property_0_comes_from_an_index_signature_so_it_must_be_accessed_with_0, unescapeLeadingUnderscores(right.escapedText));
                 }
+                if (indexInfo.declaration && getCombinedNodeFlags(indexInfo.declaration) & NodeFlags.Deprecated) {
+                    addDeprecatedSuggestion(right, [indexInfo.declaration], right.escapedText as string);
+                }
             }
             else {
                 if (isDeprecatedSymbol(prop) && isUncalledFunctionReference(node, prop) && prop.declarations) {

tests/cases/fourslash/jsdocDeprecated_suggestion17.ts

@@ -0,0 +1,31 @@
+///<reference path="fourslash.ts" />
+
+// @filename: foo.ts
+////interface Foo {
+////    /** @deprecated */
+////    [k: string]: any;
+////    /** @deprecated please use `.y` instead  */
+////    x: number;
+////    y: number;
+////}
+////function f(foo: Foo) {
+////    foo.[|x|];
+////    foo.[|y|];
+////    foo.[|z|];
+////}
+
+const ranges = test.ranges();
+verify.getSuggestionDiagnostics([
+    {
+        "code": 6385,
+        "message": "'x' is deprecated.",
+        "reportsDeprecated": true,
+        "range": ranges[0]
+    },
+    {
+        "code": 6385,
+        "message": "'z' is deprecated.",
+        "reportsDeprecated": true,
+        "range": ranges[2]
+    },
+]);