Implementing `Drop` for DOM types is being forbidden. This moves the
resource cleanup logic for `GPUSampler` to a separate
`DroppableGPUSampler` struct and removes the `allowDropImpl` flag from
the bindings configuration.
Testing: WebGpu tests just cover its cases
Fixes: Partially #26488
Signed-off-by: Domenico Rizzo <domenico.rizzo@gmail.com>