[webgpu] fixes buffer handle leak in cache manager (#23655)
### Description
There is a bug in the buffer cache manager that causes a buffer handle
leak. When the default GPU device is destroyed,
- in native, the underlying buffers are destroyed, but the handle
(specifically, the `BaseBuffer` class instance in Dawn) is not released.
This may cause small memory leaks.
- in WebAssembly, this will cause the buffers to be leaked. Both handle
(specifically, the `WGPUBufferImpl` class in emgpu) and memory will be
leaked.
This change fixes this bug by correctly assigning ownership of the
buffers using the C++ wrapper class. Destructors will be correctly
called correspondingly.
