C++: Fix more pointer/pointee conflation

[MathiasVP]

When we have IR like:

r1(glval<char **>) = VariableAddress[x]  :
r2(char **)        = Load[x]             : &:r1, m

we reuse the dataflow node for r2 to represent the dataflow node for the indirection node of r1 with indirection index 1 (i.e., the node that represents the value you get from dereferencing r1 once).

This is implemented by this disjunct in the charpred for IndirectOperand on main:

this.(OperandNode).getOperand() = Ssa::getIRRepresentationOfIndirectOperand(operand, indirectionIndex)

That is, this is used to represent the dataflow node for the indirect operand whose underlying operand is operand and whose indirection index is indirectionIndex. However, this line is only correct when indirectionIndex is 1 (because in that case the IR may have an instruction that can represent the value). If the indirection index is greater than 1, no LoadInstruction will be able to represent the dataflow node. This wasn't handled in the above disjunct, and we'd simply use the IR instruction to represent the dataflow node irregardless of the indirection index. This meant that an indirect dataflow node was being represented by an IR instruction, and meant that we got pointer/pointee conflation.

This PR fixes the conflation by using the nodeHasInstruction instruction in the above disjunction, which means that we correctly pick an IR instruction node if the indirection index is right, and otherwise we pick an indirect node.

[MathiasVP]

Here's the rundown of all the result changes.

Standard suite

dsp-testing__samate-c-cpp

cpp/cleartext-transmission

• Slight change to where the alert is highlighted. Nothing major (and it looks like this is only in a very specific case involving a strange combination of pointers and stack-buffers)

vim__vim

cpp/path-injection

• I can't seem to reproduce these two new results locally. However, that particular file has plenty of results anyway, so I'd not be surprised if this is a new TP

git-linux

cpp/use-after-free

• FP removed 🎉

openjdk-jdk

cpp/use-after-free

• FPs removed 🎉

systemd-linux

cpp/use-after-free

• FPs removed 🎉

MCTV suite

vim__vim

cpp/constant-array-overflow

(Lots of!) FPs removed 🎉

torvalds__linux

cpp/constant-array-overflow

FP removed 🎉

[rdmarsh2]

LGTM