[NFC] const-ed the return type of FunctionPropertiesAnalysis

The result is a data bag, this makes sure it's signaled to a user that
the data can't be mutated when, for example, doing something like:

auto &R = FAM.getResult<FunctionPropertiesAnalysis>(F)
...
R.Uses++

Author: mtrofin

llvm/include/llvm/Analysis/FunctionPropertiesAnalysis.h

@@ -66,7 +66,7 @@ class FunctionPropertiesAnalysis
 public:
   static AnalysisKey Key;
 
-  using Result = FunctionPropertiesInfo;
+  using Result = const FunctionPropertiesInfo;
 
   Result run(Function &F, FunctionAnalysisManager &FAM);
 };

llvm/lib/Analysis/FunctionPropertiesAnalysis.cpp

@@ -73,7 +73,7 @@ void FunctionPropertiesInfo::print(raw_ostream &OS) const {
 
 AnalysisKey FunctionPropertiesAnalysis::Key;
 
-FunctionPropertiesInfo
+const FunctionPropertiesInfo
 FunctionPropertiesAnalysis::run(Function &F, FunctionAnalysisManager &FAM) {
   return FunctionPropertiesInfo::getFunctionPropertiesInfo(
       F, FAM.getResult<LoopAnalysis>(F));