Change type of variable 'cacheable' bool to optional

The variable name of cached value was hardcoded before.
So it may be hard to expand if another meta method is added and it use cache.

So make it optional to make using cache in the other method easier.

Bug: 120158278
Test: atest android.binder.cts.NdkBinderTest
Test: m -j
Change-Id: I14aaef6c653c9e128d63083b4c8832e85f704199
1 file changed