Extend memory importer with host pointer support (#29726)
Update OrtExternalMemoryHandleType to add a new enum to allow for
importing a host pointer, similar to Vulkan and OpenCL.
### Description
This PR adds one enum for host pointers as a valid native handle type.
It also removes _VK from two existing enums to better convey that NT
handes and file descriptors are not required to be exported from Vulkan.
### Motivation and Context
There are many uses cases that benefit from importing existing
(pre-allocated) memory for use in UMA devices to eliminate copies (i.e.
zero-copy). Some examples are object detection from a camera frame,
cross API interaction (beyond DX12 and Vulkan), cross device buffer
exchange and ORT inference integration into existing pipelines to name a
few.
