Reduce number of allocation when writing string vec

We now calculate the required size of the Parcel and setDataCapacity
before writing to the parcel. This avoids needing to growData when
writing the individual strings.

This WriteListOfStrings case on Cuttlefish went from 13 allocations to
1.

Test: atest binderAllocationLimits:BinderAllocation#WriteListOfStrings
Bug: 438750707
Flag: EXEMPT bug fix
Change-Id: I51f7340bd7b9a1c011fe563166ec4f6743d3109c