When processing a JavaScript program, TS may come across a symbol that has
been imported from a TypeScript typings file.
In this case the compiler may pass the ReflectionHost a `prototype` symbol
as an export of the class.
This pseudo-member symbol has no declarations, which previously caused the
code in `Esm5ReflectionHost.reflectMembers()` to crash.
Now we just quietly ignore such a symbol and leave `Esm2015ReflectionHost`
to deal with it.
(As it happens `Esm2015ReflectionHost` also quietly ignores this symbol).
PR Close#29158
142ac41cac