[lldb] Use templates to simplify {Get,Set}PropertyAtIndex (NFC)

Use templates to simplify {Get,Set}PropertyAtIndex. It has always
bothered me how cumbersome those calls are when adding new properties.
After this patch, SetPropertyAtIndex infers the type from its arguments
and GetPropertyAtIndex required a single template argument for the
return value. As an added benefit, this enables us to remove a bunch of
wrappers from UserSettingsController and OptionValueProperties.

Differential revision: https://reviews.llvm.org/D149774

lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp

@@ -90,9 +90,8 @@ public:
   }
 
   llvm::Triple::EnvironmentType ABI() const {
-    return (llvm::Triple::EnvironmentType)m_collection_sp
-        ->GetPropertyAtIndexAsEnumeration(ePropertyABI)
-        .value_or(llvm::Triple::UnknownEnvironment);
+    return GetPropertyAtIndexAs<llvm::Triple::EnvironmentType>(
+        ePropertyABI, llvm::Triple::UnknownEnvironment);
   }
 
   OptionValueDictionary *ModuleABIMap() const {