Add bitdepth option to heif output (#4036)

Prebuilt binaries support only AVIF with a bitdepth of 8

test/unit/avif.js

@@ -144,4 +144,10 @@ describe('AVIF', () => {
       /Processed image is too large for the HEIF format/
     )
   );
+
+  it('Invalid bitdepth value throws error', async () => {
+    assert.rejects(
+      () => sharp().avif({ bitdepth: 11 }),
+      /Error: Expected 8, 10 or 12 for bitdepth but received 11 of type number/);
+  });
 });