Refactor shaders into seprate GLSL source files

The default implementation of QSGShaderMaterial::vertexShader() and
fragmentShader() now loads the GLSL source from a list of source files
that can be specified via the setShaderSourceFile() or
setShaderSourceFiles() functions.

Multiple shader source files for each shader stage are supported. Each
source file will be read in the order specified and concatenated
together before being compiled.

The other places where Qt Quick 2 loads shader source code have
been adapted to use the new QSGShaderSourceBuilder, which is also
used internally by QSGMaterial.

This puts Qt Quick 2 into a better state ready to support OpenGL
core profile and to load different shaders based upon OpenGL version,
profile, GPU vendor, platform, etc.

Change-Id: I1a66213c2ce788413168eb48c7bc5317e61988a2
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Fix hanging debug engine auto-tests

* Move the debugger agent to the same thread as the debug service. It cannot
  live in the gui thread where it is created.
* When the debugger is paused, resume immediately for now. This should be removed
  once the "counter" part propertly responds to V4_BREAK and resumes us through
  a separate message.

Change-Id: I64ea5a4e95c07763dd87736fbc72fc8927a669e3
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
QtQuick.Dialogs DefaultFontDialog: visual improvements

Layout is taller and less wide, by putting weight, style and sample
below the other list views.  It's more resolution-independent and
looks reasonable by default on Android.  Renamed Others to Style.
Made column headings bold.  Text in selected ListItem delegates
are in a contrasting color.  Delegates are taller so they are
easier to select by touch.

Task-number: QTBUG-34157
Change-Id: Ia0c96c8556835d689d3c2fd5e2c0d34e421aff76
Reviewed-by: Liang Qi <liang.qi@digia.com>