Fix infinite loop when force casting NSError to CocoaError

[nnabeyang]

This PR addresses an infinite loop issue that occurred when force casting NSError to CocoaError. The problem arose because _forceBridgeFromObjectiveC was calling _unconditionallyBridgeFromObjectiveC, and in turn, _unconditionallyBridgeFromObjectiveC was calling _forceBridgeFromObjectiveC, causing a recursive loop.

[parkera]

@swift-ci test

[parkera]

Thanks for this fix. We are strangely inconsistent about which bridging function is 'primary' for these types; sometimes it funnels to conditionally, sometimes unconditionally, sometimes none of the above.