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/scriptinterface/ScriptContext.h

@@ -56,6 +56,7 @@ public:
 		int contextSize = DEFAULT_CONTEXT_SIZE,
 		int heapGrowthBytesGCTrigger = DEFAULT_HEAP_GROWTH_BYTES_GCTRIGGER);
 
+
 	/**
 	 * MaybeIncrementalGC tries to determine whether a context-wide garbage collection would free up enough memory to
 	 * be worth the amount of time it would take. It does this with our own logic and NOT some predefined JSAPI logic because
@@ -82,7 +83,7 @@ public:
 	 * entering any compartment. It should only be used in specific situations, such as
 	 * creating a new compartment, or as an unsafe alternative to GetJSRuntime.
 	 * If you need the compartmented context of a ScriptInterface, you should create a
-	 * ScriptInterface::Request and use the context from that.
+	 * ScriptRequest and use the context from that.
 	 */
 	JSContext* GetGeneralJSContext() const { return m_cx; }