Replace JS_HasProperty + JS_GetProperty with JS_TryGetProperty

[bnoordhuis]

Problem: the JS_HasProperty + JS_GetProperty pattern shows up quite a bit and it's fairly expensive when the property exists on the prototype chain because it walks the prototype chain twice. Even when the property is on the this object, it still does double work.

Solution: add a JS_TryGetProperty that combines both operations, a la JS_TryGetPropertyInt64.

(JS_TryGetPropertyInt64 could be optimized the same way as well, by the way.)

[andrieshiemstra]

Hi, I'm looking into this and I'm wondering if we couldn't just check if JS_GetProperty (JS_GetPropertyInternal2) returns JS_UNDEFINED as building a JS_TryGetProperty would basicly be a copy of of JS_GetPropertyInternal2 and return FALSE where JS_GetPropertyInternal2 returns JS_UNDEFINED

so e.g. JS_TryGetPropertyInt64
turn this

JSValue val = JS_UNDEFINED;
    JSAtom prop;
    int present;

    if (likely((uint64_t)idx <= JS_ATOM_MAX_INT)) {
        /* fast path */
        present = JS_HasProperty(ctx, obj, __JS_AtomFromUInt32(idx));
        if (present > 0) {
            val = JS_GetPropertyValue(ctx, obj, js_int32(idx));
            if (unlikely(JS_IsException(val)))
                present = -1;
        }
    } else {

into something like this

JSValue val = JS_UNDEFINED;
    JSAtom prop;
    int present;

    if (likely((uint64_t)idx <= JS_ATOM_MAX_INT)) {
        /* fast path */
        
       val = JS_GetPropertyValue(ctx, obj, js_int32(idx));
       if (JS_VALUE_GET_TAG(val) == JS_TAG_UNDEFINED) {
            present = -1;
       } else if (unlikely(JS_IsException(val))) {
              present = -1;
	} else {
		present = 1;
	}
			
    } else {

[bnoordhuis]

check if JS_GetProperty (JS_GetPropertyInternal2) returns JS_UNDEFINED

Assuming I understand your suggestion correctly: JS_UNDEFINED is a legitimate return value (property with value undefined) so that wouldn't work. JS_UNINITIALIZED or some other sentinel that's never a valid property value perhaps could.