fix(select): improvements for announcing placeholder and value on screenreaders (#22556)

- Hides select text from screen readers so it isn't announced twice (Android talkback needs this)
- Adds the placeholder text to be announced if there is no value
- Don't add a comma if there is no value/placeholder (NVDA speech viewer)
- Don't announce alert label twice

core/src/components/select/select.tsx

@@ -458,11 +458,12 @@ export class Select implements ComponentInterface {
     const textPart = addPlaceholderClass ? 'placeholder' : 'text';
 
     // If there is a label then we need to concatenate it with the
-    // current value and a comma so it separates nicely when the screen reader
-    // announces it, otherwise just announce the value
+    // current value (or placeholder) and a comma so it separates
+    // nicely when the screen reader announces it, otherwise just
+    // announce the value / placeholder
     const displayLabel = labelText !== undefined
-      ? `${displayValue}, ${labelText}`
-      : displayValue;
+      ? (selectText !== '' ? `${selectText}, ${labelText}` : labelText)
+      : selectText;
 
     return (
       <Host
@@ -477,7 +478,7 @@ export class Select implements ComponentInterface {
           'select-disabled': disabled,
         }}
       >
-        <div class={selectTextClasses} part={textPart}>
+        <div aria-hidden="true" class={selectTextClasses} part={textPart}>
           {selectText}
         </div>
         <div class="select-icon" role="presentation" part="icon">