Cleanup, part 2

* QQmlCodeGenerator -> QQmlIR::IRBuilder (it doesn't generate code, it
generates the Object/Property/Signal/etc. IR of the .qml file, that's
going to get transformed to QV4::CompiledData::*)

* ParsedQML -> QQmlIR::Document

Change-Id: I329e858487b66e1ae528d44316761f5dd34b79f4
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Item views: improve initial Z-value handling

Respect the initial Z-values of item, highlight, header, footer and
section delegate instances. Mention also the default values in docs.

Change-Id: I2ce4bb537898a0f5fdfa776b79d5747b1c080a7b
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
Reviewed-by: Martin Jones <martin.jones@jollamobile.com>
Minor optimization: Avoid some QString constructors

Change-Id: I51af67e9ba4076216142e05b5de5b2e8f8c526bc
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Add some specialized lookups for two internal classes

Some methods are being called with two different types of objects,
alternating between them. This adds a specialized lookup for that
case. Speeds up the splay test by ~20%.

Also create a clean path to a fallback lookup instead of going back
to the generic lookup and then alternating.

Change-Id: I3082d70d27155ef5f2cf2b680d227c6dd389956d
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Small optimization to RegExp

Also add markObjects() calls to all the identifiers we keep
around in the engine. It's probably pure luck this hasn't caused
any issues until now.

Change-Id: Ie31d19793efa53867e4e240ba548070dcde32ec1
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>