Refine documentation for compilation caching.

Also let mToken in CompilationBuilder to use an array,
and add a check in NeuralNetworksWrapper on token size.

Bug: 119616526
Test: NeuralNetworksTest_static
Change-Id: Ic8d4a39cb28905bd7829ff8a39412855bb354e57
Merged-In: Ic8d4a39cb28905bd7829ff8a39412855bb354e57
(cherry picked from commit 0113aafa171c95b3cd106bd5b47d9c603c772098)
5 files changed