QPair is just an alias of std::pair anyway.

Task-number: QTBUG-115841
Change-Id: I26fc90adcc775aac9955ad57304af914dc4ed48f
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

Replace the current license disclaimer in files by
a SPDX-License-Identifier.
Files that have to be modified by hand are modified.
License files are organized under LICENSES directory.

Pick-to: 6.4
Task-number: QTBUG-67283
Change-Id: I63563bbeb6f60f89d2c99660400dca7fab78a294
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

QSGRendererInterface::OpenGLRhi is only an (undocumented) alias to
...::OpenGL, so let's use that instead.

Amends 0b2311a62b25c

Pick-to: 6.2 6.3
Change-Id: I4acdd39dc1d9b75bed5c474667a43b4ad86e7f47
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

Required three updates to examples due to some changes in
the dependency graph.

Change-Id: I48dc9bf6d4fa82395bdf25deb1a768c354097bdc
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

Also enable the two Metal-specific scenegraph examples on iOS.

Change-Id: I0e1e6d527544ea4a5bfb0d08ca2d32c762d3c699
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

Change-Id: I715ad71153151a0e6521bc182227d9fa2dc0a3ea
Reviewed-by: Christian Strømme <christian.stromme@qt.io>

Change-Id: I8973798996b6c775f425819af1d6a09f1773a9dc
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

Opt in via environment variables:
QSG_RHI=1 -> enable using QRhi instead of GL
QSG_RHI_BACKEND -> set to vulkan, metal, d3d11, gl to override the default
(the default is d3d11 on Windows, metal on Mac, gl elsewhere)

Or force a given rhi backend via the existing
QQuickWindow::setSceneGraphBackend().

Otherwise the default behavior is the same as before, the rhi code path
is never active by default.

-no-opengl builds are supported in the sense that they work and default
to the software backend. However, the rhi code path cannot currently be
used in such builds, even though QRhi from qtbase is fully functional
with Vulkan, D3D, or Metal even when qtbase was configured with
-no-opengl. This cannot be utilized by Quick atm due to OpenGL usage
being all over the place in the sources corresponding to the default
backend, and those host the rhi code path as well. This will be cleaned up
hopefully in Qt 6, with the removal all direct OpenGL usage.

Other env.vars.:
QSG_RHI_DEBUG_LAYER=1 -> enable D3D debug or Vulkan validation layer
(assuming the system is set up for this)
QSG_RHI_SHADEREFFECT_DEBUG=1 -> print stuff from ShaderEffect
QSG_SAMPLES=1,2,4,... -> MSAA sample count (but QSurfaceFormat works too)
QT_D3D_ADAPTER_INDEX=0,1,... -> D3D adapter index
QT_VK_PHYSICAL_DEVICE_INDEX=0,1,... -> Vulkan physical device index
QSG_RHI_UINT32_INDEX=1 -> always use uint index data (both
merged/unmerged, convert when needed - with some rhi backends this is
implicit)
QSG_RENDER_LOOP -> to override the render loop as usual. The default
with RHI is threaded for Metal, threaded for Vulkan on Windows, basic
for Vulkan on Linux and Android (to be checked later), while the existing
rules apply for OpenGL.

Not supported when running with QRhi:
  - particles
  - compressed atlases (though this is transparent to the apps)
  - QSGRenderNode
  - QQuickRenderControl
  - QQuickFramebufferObject
  - certain QQuickWindow functionality that depends directly on OpenGL
  - anisotropic filtering for textures
  - native text may lack some gamma correction
  - QSGEngine applicability unclear
  - some QML profiler logs may be incorrect or irrelevant

Change-Id: I7822e99ad79e342e4166275da6e9e66498d76521
Reviewed-by: Lars Knoll <lars.knoll@qt.io>