When creating synthetic default symbol set parent as module symbol

[sheetalkamat]

Fixes #40684

[andrewbranch]

This matches the structure of non-synthetic default export symbols, right? As long as that’s the case, makes sense

[weswigham]

Uh, this is probably OK, so long as nothing's expecting symbol.parent.members or symbol.parent.exports actually contains symbol... The real parent should probably be the anonymousSymbol defined below, since that's the symbol whose (associated type's) members table actually contains this symbol, at least that's what I'd have thought.

[sheetalkamat]

@weswigham this is mainly so that this synthetic default has parent similar to what happens when you have written default declaration in the file. Without this it would be hard to figure out moduleSymbol from this synthetic default