nativewindow: Misc. improvements for AHardwareBuffer Rust wrapper

Changes include:

  - Rename AHardwareBuffer to HardwareBuffer
  - Expose AHardwareBuffer as a raw pointer type
  - Making HardwareBuffer Send
  - HardwareBuffer now derives Debug, PartialEq and Eq
  - Use NonNull instead of a *mut pointer
  - Adding an into_raw function to match from_raw
  - Adding a Clone impl that acquires a ref

Bug: 296449936, 296100790
Test: atest libnativewindow_rs-internal_test
Change-Id: Iaf916fabe49190f47abd1a9ed34afdb76fd20e40