Changes regarding naming and API consistency

[marc0246]

Changelog:

- Changes to `StandardCommandPool`:
  - **Breaking** `Device::standard_command_pool` has been removed in favor of `Device::with_standard_command_pool`.
- **Breaking** Changes to `StdMemoryPool`:
  - Renamed `StdMemoryPool[Alloc]`, `StdHostVisibleMemoryTypePool[Alloc]`, `StdNonHostVisibleMemoryTypePool[Alloc]` to `Standard{...}`.
  - Removed `Device::standard_pool` in favor of `Device::standard_memory_pool`.
- **Breaking** Changes to `StdDescriptorPool`:
  - Renamed `StdDescriptorPool[Alloc]` to `Standard{...}`.

• Following up on StdDescriptorPool rewamp #1943, the way StandardCommandPool is accessed has been made consistent with StdDescriptorPool, which avoids cloning an Arc unneccessarily each time the pool is accessed.
• Renamed Std* types to Standard* for consistency.
• Device::standard_pool has changed signature and was renamed, so that it is more idiomatic and consistent with the rest of the API.
• Import granularity across the crate has been made consistent.

[Rua]

It all looks good, thank you for helping keep Vulkano fast and consistent!

[marc0246]

No thank you ma'am, for all your hard work on maintenance!