Improve JS Exception handling.

- Check for pending exceptions after function calls and script
executions.
- Call LOGERROR instead of JS_ReportError when there is a conversion
error in FromJSVal, since that can only be called from C++ (where JS
errors don't really make sense). Instead, C++ callers of FromJSVal
should handle the failure and, themselves, either report an error or
simply do something else.
- Wrap JS_ReportError since that makes updating it later easier.

This isn't a systematical fix since ToJSVal also ought return a boolean
for failures, and we probably should trigger errors instead of warnings
on 'implicit' conversions, rather a preparation diff.

Part of the SM52 migration, stage: SM45 compatible (actually SM52
incompatible, too).

Based on a patch by: Itms
Comments by: Vladislavbelov, Stan`
Refs #742, #4893

Differential Revision: https://code.wildfiregames.com/D3093
This was SVN commit r24187.

source/ps/SavedGame.cpp

@@ -52,7 +52,7 @@ Status SavedGames::SavePrefix(const CStrW& prefix, const CStrW& description, CSi
 
 Status SavedGames::Save(const CStrW& name, const CStrW& description, CSimulation2& simulation, const shared_ptr<ScriptInterface::StructuredClone>& guiMetadataClone)
 {
-	ScriptInterface::Request rq(simulation.GetScriptInterface());
+	ScriptRequest rq(simulation.GetScriptInterface());
 
 	// Determine the filename to save under
 	const VfsPath basenameFormat(L"saves/" + name);
@@ -226,7 +226,7 @@ Status SavedGames::Load(const std::wstring& name, const ScriptInterface& scriptI
 JS::Value SavedGames::GetSavedGames(const ScriptInterface& scriptInterface)
 {
 	TIMER(L"GetSavedGames");
-	ScriptInterface::Request rq(scriptInterface);
+	ScriptRequest rq(scriptInterface);
 
 	JS::RootedValue games(rq.cx);
 	ScriptInterface::CreateArray(rq, &games);