Add baseline scene for instancingLodFactor level selection

Replace lod_mixed_shapes.mesh with lod_digits.mesh, whose levels are
extruded digits: the original is a "0" and levels 1 to 9 are "1" to "9",
so every render labels the LOD level it picked. The old file had its
original range spanning the whole index buffer, overlapping every LOD
range, all-zero subset bounds, and a level 1 distance of 0 that made the
original unreachable for distance based selection. The new file is laid
out like Balsam output, coarsest level first and the original last, with
16-bit indices and computed bounds. Its distances start at 0.65 and 1.05
so camera/LevelOfDetail shows 0, 1 and 2 at 800x480, and grow
geometrically from there.

Add LodFactorLevel0.qml: the mesh drawn with flat colours non-instanced
with LOD disabled, then instanced with instancingLodFactor stepping from
0 to 1 in ninths. The expected row is 0 0 1 2 3 4 5 6 7 8 9. Currently
it is 0 1 2 3 4 5 5 6 7 8 9, because the original is unreachable through
the manual factor and the factor is spread over one level too few, which
the following fix addresses.

Task-number: QTBUG-151352
Pick-to: 6.12
Assisted-by: Claude Code Fable 5.1
Change-Id: I0cab39bd6117250d560155cebfa4c0b0ed565931
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
Reviewed-by: Andrei Yankovich <EndrIIMail@gmail.com>