[SYCL][Bindless] Add mipmap interop + slight redesign + bug fix

[Seanst98]

Mipmap interop:

• Remove "interop" image type as it is redundant for image creation
• Add a vulkan mipmap interop test

Slight redesign:

• Simplify external resources

Modify the bindless spec to reflect these changes

Fix Vulkan interop tests to prevent memory leak issue by freeing mapped memory

Corresponding UR PR: https://github.com/oneapi-src/unified-runtime/pull/1351