This makes two changes to how example exprs are selected. Example exprs
are now ordered separately by each piece of the location, rather than by
stringifying their location. Second, UnknownLocations are now ordered
after locations with absolute paths, by using "~" in the lexicographic
comparison of absolute paths. I think this works on both POSIX and
Windows systems, but it's possible I'm missing a way to start an
absolute path with a unicode character.
Instead of computing these two things in one predicate, they are
computed in separate predicates and then joined. This splits the
predicate `getInstruction`, which took 81s before, into predicates that
together take 20s on a medium-sized db.
Moved IR flavors into "implementation", with internal files under "implementation/internal". Made `IRBlockConstruction` just a nested module of `IRConstruction`/`SSAConstruction`, so it gets picked up from the `Construction` parameter of the `IR` module, rather than being picked up just from being in the same directory as `IRBlock`.
This change makes the public IR.qll module resolve to the flavor of the IR that we want queries to use. Today, this is the aliased SSA flavor of the IR. Should we add additional IR iterations in the future, we'll update IR.qll to resolve to whichever one we consider the default.
I moved the PrintIR.ql and IRSanity.ql queries into the internal directories of the corresponding flavors. There's still a PrintIR.ql and an IRSanity.ql in the public IR directory, which use the same IR flavor as the public IR.qll.
There are no real code changes here, other than to fix up `import`s. All tests still hae the same output, as expected.
A future commit will hide the IR flavors other than the one we want queries to use directly.
