refactor(material/timepicker): adds check for aria-labelledby for override

Updates previous fix which implements a default aria-label if no custom
aria-label is provided to where it checks if an aria-lablledby value is
provided and uses the aria-labelledby value if available. If not it will
check for a custom aria-label and if that is not provided it will default
to the generic aria-label value.

Author: essjay05

src/material/timepicker/timepicker-toggle.ts

@@ -94,11 +94,10 @@ export class MatTimepickerToggle<D> {
   }
 
   /**
-   * Gets the aria-label to use for the toggle button.
-   * Returns the user-provided aria-label if one exists,
-   * otherwise returns the default aria-label using the timepicker's panelId.
+   * Checks for ariaLabelledby and if empty uses custom
+   * aria-label or defaultAriaLabel if neither is provided.
    */
-  getAriaLabel(): string {
-    return this.ariaLabel() || this._defaultAriaLabel;
+  getAriaLabel(): string | null {
+    return this.ariaLabelledby() ? null : this.ariaLabel() || this._defaultAriaLabel;
   }
 }

tools/public_api_guard/material/timepicker.md

@@ -127,7 +127,7 @@ export class MatTimepickerToggle<D> {
     readonly ariaLabelledby: InputSignal<string | undefined>;
     readonly disabled: InputSignalWithTransform<boolean, unknown>;
     readonly disableRipple: InputSignalWithTransform<boolean, unknown>;
-    getAriaLabel(): string;
+    getAriaLabel(): string | null;
     // (undocumented)
     protected _isDisabled: Signal<boolean>;
     protected _open(event: Event): void;