Select - no longer update value while navigating dropdown (#2029)

# Pull Request

## 🤨 Rationale

While in the midst of implementing the [clear
select](#1951) feature, I recognized
that the fact that we were updating the value while navigating the
dropdown was both confusing (since we don't update the display value)
and resulting in an awkward implementation for the feature.

change/@ni-nimble-components-9da2496e-e544-4019-a666-d7fca3046771.json

@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "Change Select to not update value as you navigate options in dropdown.",
+  "packageName": "@ni/nimble-components",
+  "email": "26874831+atmgrifter00@users.noreply.github.com",
+  "dependentChangeType": "patch"
+}

packages/nimble-components/src/list-option/index.ts

@@ -41,6 +41,17 @@ export class ListOption extends FoundationListboxOption {
     @attr({ attribute: 'visually-hidden', mode: 'boolean' })
     public visuallyHidden = false;
 
+    /**
+     * @internal
+     * This attribute is used to control the visual selected state of an option. This
+     * is handled independently of the public 'selected' attribute, as 'selected' is
+     * representative of the current value of the container control. However, while
+     * a dropdown is open users can navigate through the options (requiring visual
+     * updates) without changing the value of the container control.
+     */
+    @attr({ attribute: 'active-option', mode: 'boolean' })
+    public activeOption = false;
+
     /** @internal */
     @observable
     public hasOverflow = false;