Allow a Partial object for labels in MultiSelect (#2843)

## Summary:
This allows consumers to decide which labels to override, as some may not be relevant and some may be deliberately left as their default values.

## Test plan:
Verify types pass on stories and stories still render as expected

Author: timmcca-be

Reviewers: jandrade

Required Reviewers:

Approved By: jandrade

Checks: ✅ 20 checks were successful, ⏭️  4 checks have been skipped, ⏹️  2 checks were cancelled

Pull Request URL: #2843

Author: timmcca-be

.changeset/sharp-pans-try.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/wonder-blocks-dropdown": minor
+---
+
+Allow a `Partial` object for `labels` in `MultiSelect`, so consumers can decide which labels to override

__docs__/wonder-blocks-dropdown/multi-select.stories.tsx

@@ -15,7 +15,6 @@ import type {LabelsValues} from "@khanacademy/wonder-blocks-dropdown";
 import ComponentInfo from "../components/component-info";
 import packageConfig from "../../packages/wonder-blocks-dropdown/package.json";
 import multiSelectArgtypes from "./multi-select.argtypes";
-import {defaultLabels} from "../../packages/wonder-blocks-dropdown/src/util/constants";
 import {
     allCountries,
     allProfilesWithPictures,
@@ -340,8 +339,7 @@ export const ControlledOpened: StoryComponentType = {
 };
 
 // Custom MultiSelect labels
-const dropdownLabels: LabelsValues = {
-    ...defaultLabels,
+const dropdownLabels: Partial<LabelsValues> = {
     noneSelected: "Solar system",
     someSelected: (numSelectedValues: number) => `${numSelectedValues} planets`,
 };
@@ -651,7 +649,6 @@ export const ImplicitAllEnabled: StoryComponentType = {
     args: {
         implicitAllEnabled: true,
         labels: {
-            ...defaultLabels,
             someSelected: (numSelectedValues: number) =>
                 `${numSelectedValues} fruits`,
             allSelected: "All planets selected",

packages/wonder-blocks-dropdown/src/components/multi-select.tsx

@@ -132,7 +132,7 @@ type Props = AriaProps &
         /**
          * The object containing the custom labels and placeholder values used inside this component.
          */
-        labels?: LabelsValues;
+        labels?: Partial<LabelsValues>;
         /**
          * Callback for when the selection changes. Parameter is an updated array of
          * the values that are now selected.