Speed up stack trace generation for the JIT

It turns out that in QML it is not unusual that during early binding
evaluations due to the undefined order, the evaluation tries to look up
properties in objects that aren't initialized yet and thus exceptions are
thrown. Eeach thrown exception saves a stack trace, which is expensive to
generate when using the JIT, as it does full stack unwinding.

This patch implements a more light-weight approach by storing the instruction
pointer in the context before leaving JIT generated code.

Change-Id: I95e1cfd01179247dfc2c1df949828f474a23161b
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Speed up exception propagation

Avoid catch (...) with re-throw as it turns that this is very slow because it
throws a new exception and the unwinder starts from scratch. Instead use stack
allocated objects and cleaning destructors to restore state before continuing
with the propagation of exceptions.

Change-Id: I6d95026bcd60b58cb6258a9dae28623a46739532
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix performance regression when doing property lookups for non-existant properties

Commit 84627464eb11ca1149d46946b12e3c82eb54a8bf introduced a performance
regression of falling back to reading the QMetaObject, when the lookup for a
property in QML failed, after we've tried in the property cache. This is very
very expensive to do and was only due to QQmlPropertyMap not correctly
invalidating the property cache.

Instead remove the property cache from the property map's QObject and on the
lookup side rely on the property cache being correct in the result (positive or
negative).

Change-Id: I8a013483203f2007d48b71feafa10b3ea02c53fd
Reviewed-by: Lars Knoll <lars.knoll@digia.com>