[analysis] FunctionAnalysisBase's parameter SILAnalysisTy is actually…

[gottesmm]

… a FunctionInfoTy.

I believe that this was just a typo from a long time ago. Calling this parameter
a SILAnalysisTy is actively misleading since as a result it seems to a naive
reading that one should be writing a recursive template:

class MyAnalysis : public FunctionAnalysisBase<MyAnalysis> { ... }

Instead of passing in the function info of the derived analysis, i.e.:

class MyAnalysisFunctionInfo { ... }
class MyAnalysis : public FunctionAnalysisBase<MyAnalysisFunctionInfo> { ... }

I also added some documentation to that effect onto FunctionAnalysisBase.

[gottesmm]

@swift-ci smoke test and merge