[clang] [clang][analyzer] Add notes to PointerSubChecker (PR #95899)

[Balázs Kéri via cfe-commits]

balazske wrote:

I found difficult results from the checker where it is not obvious what the problem is.
One type is this case where a negative index is found (any of these results, or check the first one):
https://codechecker-demo.eastus.cloudapp.azure.com/Default/reports?run=curl_curl-7_66_0_pointersub&is-unique=off&diff-type=New&checker-name=alpha.core.PointerSub
This type of problem is not fixed with the patch.

Other problem is when different arrays are found:
https://codechecker-demo.eastus.cloudapp.azure.com/Default/report-detail?run=vim_v8.2.1920_pointersub&is-unique=off&diff-type=New&checker-name=alpha.core.PointerSub&report-id=5494864&report-hash=9a4c8e84e0c5227d61f321ec217e88ec&report-filepath=%2Flocal%2Fpersistent_docker%2FCSA-measurements-driver-2913%2Fmeasurements_workspace%2Fvim%2Fsrc%2Fevalvars.c
This case should improve with the patch (but not tested yet).

https://github.com/llvm/llvm-project/pull/95899