Refactor instruction folders (#2815)

* Refactor instruction folders

We want to refactor the instruction folder to allow different sets of
rules to be added to the instruction folder.  We might want different
sets of rules in different circumstances.

We also need a way to add rules for extended instructions.  Changes are
made to the FoldingRules class and ConstFoldingRules class to enable
that.

We added tests to check that we can fold extended instructions using the
new framework.

At the same time, I noticed that there were two tests that did not tests
what they were suppose to.  They could not be easily salvaged. #2813 was
opened to track adding the new tests.