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/network/NetServer.cpp

@@ -418,7 +418,7 @@ bool CNetServerWorker::RunStep()
 
 	m_ScriptInterface->GetContext()->MaybeIncrementalGC(0.5f);
 
-	ScriptInterface::Request rq(m_ScriptInterface);
+	ScriptRequest rq(m_ScriptInterface);
 
 	std::vector<bool> newStartGame;
 	std::vector<std::string> newGameAttributes;
@@ -1136,7 +1136,7 @@ bool CNetServerWorker::OnSimulationCommand(void* context, CFsmEvent* event)
 	// unless cheating is enabled
 	bool cheatsEnabled = false;
 	const ScriptInterface& scriptInterface = server.GetScriptInterface();
-	ScriptInterface::Request rq(scriptInterface);
+	ScriptRequest rq(scriptInterface);
 	JS::RootedValue settings(rq.cx);
 	scriptInterface.GetProperty(server.m_GameAttributes, "settings", &settings);
 	if (scriptInterface.HasProperty(settings, "CheatsEnabled"))