Fix failing assertion with MSVC in debug builds in various tests

Fix failing assertion with MSVC in debug builds in various tests

We re-implemented Vector::begin() and end() by means of dereferencing the return
value from std::begin() and then taking the address of it. That causes a failing
assertion in MSVC's STL (rightly so!). We did this only to avoid modifying
the original YarrJIT.cpp code.

This patch instead simplifies our Vector.h stub again and just fixes the two
small occurrences in YarrJIT.cpp where it expects vector->begin() to return a
pointer instead of an iterator.

Change-Id: I2ad137be91ea969ccb310333dffa8d98e5825f8f
Reviewed-by: Lars Knoll <lars.knoll@digia.com>