[incfs] Preallocate space for IncFS files

Use the new libincfs APIs to preallocate space for all files
created via the public makeFile() API. This way we ensure
the device won't run out of space much later

Bug: 182185202
Test: atest libincfs-test PackageManagerShellCommandTest \
 PackageManagerShellCommandIncrementalTest \
 IncrementalServiceTest
Change-Id: I70af97949b29ff5db63201b0e3487fe026e23160