Codec2: Add C2Fence returnable fetch interfaces to C2BlockPool

Add new fetch interfaces to C2BlockPool. The interfaces will return a
C2Fence as an output parameter. C2Fence can be waited until fetch is not
blocked anymore.

Bug: 157111613
Change-Id: I691b3605a63724b29a8fcb4c9327cb52285d1086
Merged-In: I691b3605a63724b29a8fcb4c9327cb52285d1086
1 file changed