Mark pipeline compilation of ubershaders as high priority.

[DarioSamo]

Sanitizes the behavior seen in #101844.

In projects with high contention of threads in the worker pool, pipeline compilation for ubershaders takes an unnecessary backseat and can cause significant delays in the main thread. This PR marks compilation of any ubershader pipelines as high priority to mitigate this issue.

As indicated to the OP however, the issue itself is a bit more of a content issue, but regardless, the improvement should help in scenarios where it is critical for the game to be responsive compared to other tasks that might've been launched by the project.

We should probably test for no regressions in loading times to be found on existing projects when using no pipeline cache and clean driver caches.

Bugsquad edit: Fixes: #101844

[clayjohn]

Tested with the MRP from #101844 this reduces the lag from compiling significantly (1750 ms -> 6 ms). For me thats enough to say that this fixes #101844

Compiling at runtime is not ideal and users should expect a pipeline stutter when doing surface compilations. Accordingly, this PR doesn't "fix" the stutter in #101844. However, it does reduce the stutter to an acceptable degree (assuming the user was okay with the stutter in 4.3). Therefore, it is safe to say that this fixes #101844. In other words the bug in #101844 is just that the stutter was worse, this fixes the bug, even though it doesn't eliminate the stutter entirely

[Repiteo]

Thanks!