Refine builder and rafs to prepare for tarfs#1144

Merged

imeoer merged 3 commits intodragonflyoss:masterfrom jiangliu:prepare-tarfs

Mar 13, 2023

+196-156

Commits on Mar 9, 2023

rafs: rename EROFS_BLOCK_SIZE to EROFS_BLOCK_SIZE_4096
jiangliu
committed

Commits on Mar 12, 2023

rafs: replace with_context() by context() when possible
jiangliu
committed

Commits on Mar 13, 2023

rafs: only invoke v5 related code for v5 builds
jiangliu
committed