Merge pull request #15980 from MathiasVP/guards-lt

C++: Support `<` reasoning for `switch` statements in Guards library

Author: MathiasVP

cpp/ql/lib/change-notes/2024-03-19-predicates-for-switches-as-guards-2.md

@@ -0,0 +1,5 @@
+---
+category: feature
+---
+* Added a predicate `GuardCondition.comparesLt/4` to query whether an expression is compared to a constant. 
+* Added a predicate `GuardCondition.ensuresLt/4` to query whether a basic block is guarded by an expression being less than a constant.