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/scripting/JSInterface_SavedGame.cpp

@@ -78,7 +78,7 @@ JS::Value JSI_SavedGame::StartSavedGame(ScriptInterface::CmptPrivate* pCmptPriva
 	// The GUI calls this function from the GUI context and expects the return value in the same context.
 	// The game we start from here creates another context and expects data in this context.
 
-	ScriptInterface::Request rqGui(pCmptPrivate);
+	ScriptRequest rqGui(pCmptPrivate->pScriptInterface);
 
 	ENSURE(!g_NetServer);
 	ENSURE(!g_NetClient);
@@ -96,7 +96,7 @@ JS::Value JSI_SavedGame::StartSavedGame(ScriptInterface::CmptPrivate* pCmptPriva
 
 	{
 		CSimulation2* sim = g_Game->GetSimulation2();
-		ScriptInterface::Request rqGame(sim->GetScriptInterface());
+		ScriptRequest rqGame(sim->GetScriptInterface());
 
 		JS::RootedValue gameContextMetadata(rqGame.cx,
 			sim->GetScriptInterface().CloneValueFromOtherCompartment(*(pCmptPrivate->pScriptInterface), guiContextMetadata));