Opportunisticly emit compact imports (#8926)

In the binary writer when compact imports are enabled, opportunistically
look for pairs of adjacent imports that share both their module names
and import types, or alternatively just their module names. When a pair
of matching imports is found, create a run of compact imports that
includes as many subsequent imports as possible. Adding a pass that will
reorder imports to purposefully put similar imports together is left as
future work.