Issue serialization error when attempting to serialize a late-bound name from a mapped type

[weswigham]

Fixes #49065 - we now consistently issue an error on the mapped type form of the declaration, just like the anonymous object declaration. (Late bound names fed into mapped types don't get CheckFlags.Late set on them because they didn't go through the late binding process, however our output of the type will, so the name being a late bindable name alone is sufficient to need to issue the error)

[andrewbranch]

Makes sense in terms of doing the same thing as the object type declaration, but why can’t this one serialize as typeof import("./a").Timestamp?

[weswigham]

That would be valid in a type position, but computed property names are value positions, and our only logic for a value position is "preserve what the user wrote", except because this name came from a mapped type, the user wrote nothing, so there's nothing we can preserve.

[sandersn]

@weswigham does this need more review or is it ready to merge?