Add retry mechanism for clipboard tests

[LeafShi1]

Refer to PR #12087

In order to confirm that clipboard operation can be executing more stable, we consider add retry mechanism for clipboard tests

[JeremyKuhne]

The right way to handle this is to make sure they are all in the same test collection fixture. Sleeping before testing won't help. This is a place we need a retry mechanism.

[JeremyKuhne]

Anything using drag/drop APIs also cannot be run asynchronously and should be in the same collection.

[JeremyKuhne]

[UISettings(MaxAttempts = )] should let you do retries. It was added to Xunit.StaFact last year, need v1.2.46-alpha, which we're already consuming.

[paul1956]

@JeremyKuhne is there a recommend value to MaxAttempts for clipboard tests. All clipboard test are in at least 4 different classes but all Sequential tests are in the one Collection(“Sequential”), this includes unrelated tests for WebBrowser.

[JeremyKuhne]

3 is probably reasonable to start, but we can go higher in this particular case (OLE).

[Tanya-Solyanik]

@LeafShi1 - could you please verify if all clipboard tests, even from other test assemblies, are using the same mechanism.