[0.7/dx12] Reset command allocators periodically

[grovesNL]

Backport #3680 to hal-0.7 to avoid excess memory usage in DX12.

Some Bevy users were hitting this through wgpu, so it might be nice to backport this fix this in 0.7 too (instead of waiting for the next wgpu release).

I tried hal-0.7 with and without the fix on quad by repeatedly resizing the window, and the memory grows without the fix but seems stable with it (as expected).

PR checklist:

• [ ] make succeeds (on *nix)
• [ ] make reftests succeeds
• [X] tested examples with the following backends: DX12

[bors[bot]]

Build succeeded:

• Android Stable
• Dependency Check
• iOS Stable
• MacOS Nightly
• MacOS Stable
• Ubuntu Nightly
• Ubuntu Stable
• Web Assembly
• Windows Nightly
• Windows Stable

[kvark]

This is published in 0.7.1 now 🚀

[grovesNL]

Thank you!