If a decorated class is not publicly exported via an entry-point then the
previous approach to finding the associated typings file failed.
Now we ensure that we extract all the class declarations from the
dtsTypings program, even if they are not exported from the entry-point.
This is achieved by also parsing statements of each source file, rather
than just parsing classes that are exported from the entry-point.
Because we now look at all the files, it is possible for there to be multiple
class declarations with the same local name. In this case, only the first
declaration with a given name is added to the map; subsequent classes are
ignored.
We are most interested in classes that are publicly exported from the
entry-point, so these are added to the map first, to ensure that they are
not ignored.
PR Close#26906