Add BufferHub-based IGBC implementation

This is mostly a placeholder to create an IGBC/IGBP pair based on
BufferHub for testing purpose. A fully functional implementation will be
filled in later.

Bug: 72972441
Bug: 70046255
Test: libgui_test
Change-Id: I2215bd78da1d0104f2cbb9599f874c810898be56