The bytecode reader currently assumes all regions can be lazy
loaded, which breaks reading any non-isolated region. This patch
fixes that by properly handling nested non-lazy regions, and only
considers isolated regions as lazy.
Differential Revision: https://reviews.llvm.org/D153795
IsolatedRegions are emitted in sections in order for the reader to be
able to skip over them. A new class is exposed to manage the state and
allow the readers to load these IsolatedRegions on-demand.
Differential Revision: https://reviews.llvm.org/D149515