Use Module#ancestors order in recursive constant lookup

[XrXr]

Before this commit, const_get with inherit=true and constant lookup
expressions searched the ancestors of the starting point in an order
different from starting_point.ancestors.

Items in the ancestry list introduced through prepend were
searched after searching the module they were prepended into. This
oddity allowed for situations where constant lookups gave different
results even though starting_point.ancestors is the same.

Do the lookup in the same order as starting_point.ancestors by
skipping classes and modules that have an origin iclass. The origin
iclass is in the super chain after the prepended modules.

Note that just like before this commit, the starting point of the
constant lookup is always the first item that we search, regardless of
the presence of any prepended modules.

[Bug #17887]

[jeremyevans]

This is much simpler than my approach in #4538. I also think you are correct about the handling of the inherit argument, since that is more consistent with how method_defined? works. Great work! As long as this passes CI, I'll close #4538.