1. The new query is expecting pointer arithmetic operations to generate
range-analysis bounds, but this wasn't true on main.
2. The bounds generated by `boundFlowCond` was incorrectly inferred as
non-strict when comparing a pointers (unlike when comparing values of
integral types). This gave FPs in the new query.
This also fixes a couple of missing results in existing queries that
use the new range-analysis library.
Just to demonstrate how things fit together, I've created
`SubtractSelf.qll` that adds a (hopefully sound) version of the test
extension that was already used in `extensibility.ql`.
It does so by first defining what a pointer dereference is (on the IR
`Instruction` level), and then using the array length analysis and the range
analysis together to prove that some of these pointer dereferences are safe.
For each pointer, we start tracking (starting from the allocation or an array declaration)
1) how long is the chunk of memory allocated
2) where the current pointer is in this chunk of memory.
This information might not always exist, but when it does, it is reliable.
Currently only works intraprocedurally.
