Refactor IRBuilder to build blocks internally (#5901)

The initial PR introducing IRBuilder kept the interface the same as the previous
internal interface in the new wat parser. This PR updates that interface to
avoid exposing implementation details of the IRBuilder and to provide an API
that matches the binary format. For example, after calling `makeBlock` or
`visitBlock` at the beginning of a block, users now call `visitEnd()` at the end
of the block without having to manually install the block's contents.

Providing this improved interface requires refactoring some of the IRBuilder
internals. While we are refactoring things anyway, put in extra effort to avoid
unnecessarily splitting up and recombining tuples that could simply be returned
from a multivalue block.

0 files changed, 0 insertions, 0 deletions