drm_hwcomposer: refactor platform directory

Motivation:

Platform term meaning used in drm_hwcomposer does not correspond to the
content of the platform directory. Platform directory consists of:
1. Buffer information getters for different gralloc (currently called platform).
2. Composition planner logic (which has flaws and should be reworked into
   layer->plane mapping during validation stage logic).
3. DrmGenericImpoter with reference counting logic.

Android-11 IMapper@4 metadata API offers a generic way to access buffer
information which makes other gralloc buffer information getters obsolete.
Legacy getters should be maintained for some time until all known users
will migrate to Mapper@4 API.

Implementation:

1. Split 'PlatformImporter' logic to 'Importer' only and 'Buffer Getter' logic.
   a. Remove buffer_handle_t parameter from ImportBuffer(). Instead user should
      get BufferInfo using ConvertBoInfo to struct hwc_drm_bo_t, then use it for
      ImportBuffer().
   b. Move DrmGenericImporter.{cpp/h} into the drm directory.

2. Isolate planner code in single file and move it to compositor directory as
   compositor/Planner.{cpp/h}

3. Rename platform definition
   a. Rename platform directory to bufferinfo.
   b. Rename/move bufferinfo/platorm*.{cpp,h} getters to
      bufferinfo/legacy/BufferInfo*.{cpp,h}. Align class names/includes.

4. Split legacy/metadata getters logic.
   a. Apply existing bufferinfogetter base class only for legacy getters.
   b. Combine legacy/generic gettera under new base class.
   c. Create a placeholder for generic(metadata) getter.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/backend/Backend.cpp b/backend/Backend.cpp
index 50ef900..887eb0e 100644
--- a/backend/Backend.cpp
+++ b/backend/Backend.cpp
@@ -17,6 +17,7 @@
 #include "Backend.h"
 
 #include "BackendManager.h"
+#include "bufferinfo/BufferInfoGetter.h"
 
 namespace android {
 
@@ -125,7 +126,7 @@
 bool Backend::IsClientLayer(DrmHwcTwo::HwcDisplay *display,
                             DrmHwcTwo::HwcLayer *layer) {
   return !display->HardwareSupportsLayerType(layer->sf_type()) ||
-         !display->importer()->CanImportBuffer(layer->buffer()) ||
+         !BufferInfoGetter::GetInstance()->IsHandleUsable(layer->buffer()) ||
          display->color_transform_hint() != HAL_COLOR_TRANSFORM_IDENTITY ||
          (layer->RequireScalingOrPhasing() &&
           display->resource_manager()->ForcedScalingWithGpu());