* More precise property-overwritten-by-spread errors
Trying to do this check in getSpreadType just doesn't have enough
information, so I moved it to checkObjectLiteral, which is a better
place for issuing errors anyway.
Unfortunately, the approach is kind of expensive in that it
1. creates a new map for each property and
2. iterates over all properties of the spread type, even if it's a
union.
I have some ideas to improve (1) that might work out. I'm not sure how
bad (2) is since we're going to iterate over all properties of all
constituents of a union.
Fixes#36779
* another test and rename
b481dd4d4b