Visit default export expressions in module visitor

[weswigham]

Fixes #18968

[mhegazy]

Can you do an audit on this file, and make sure we are transpiling imports in all places, this is the third issue we have had to deal with regarding this.

[weswigham]

@mhegazy I just grep'd the file for all node. instances, I found one more obvious issue involving nested imports (await import(await import("foo")), opened #18982 - issue seems to actually be with the generator transform, but it may compound with the module transform), and then by chance also found #18981. Besides those, at this point it looks like all remaining node references in the module transformer are either leaf nodes (modifiers, operators), or get visited. The whole "manually interleave multiple logical visitors to attempt to get better perf" makes it difficult to track. It'd be nicer if we just had a function for composing independent transforms into a single walk.

[weswigham]

Also, @mhegazy does this need to be ported to the 2.6 branch?

[DanielRosenwasser]

@weswigham yup, it'll just go after the RC.

[mhegazy]

Also, @mhegazy does this need to be ported to the 2.6 branch?

I will do a merge from master next week.

[weswigham]

Got it, won't port anything explicitly until then, then.