Fix T68826 Eevee: Multi-Mat not working if switching from Solid shading

The correct fix would be to avoid all those hacks but this is needed if
we want to be able to parallelize object vbo extractions.

GPU: Fix Element index range calculation

Fix T68880 2D line display is broken

Fix T68837 Eevee: Fix "GPU failed to find function math_max" message

Was a missing rename.

Mesh Batch Cache: Fix crash caused by rB3cbf2462391c

Fix T68719 Viewport: Wrong material index when switching between view mode

This was due to the GPUIndexBuf ranges only computed when requesting
the triangles indices. If the tris were already calculated, the new shading
batches would never have the GPUIndexBuf ranges and instead use the full
triangle index buffer.

So since this only happen when shading data does not match, we just save
the previous GPUIndexBuf ranges and reuse them for the new batch.

This patch is a bit of a hack on top of a hack but it works fine.

Mesh Batch Cache: Fix regression with mesh that have poly mat id > mat_len

DRW: Fix couple of issues in DRW_draw_select_id

Theses 2 function calls are mandatory.

DRW: Add DRWCommandSetStencil

Now multiple stencils can be set inside a shgroup.

Should not change the previous behavior as all usage of
DRW_shgroup_stencil_mask was done at shgroup creation.

DRW: Move DRWUniformChunk length and used counter to the struct itself.

This is better for code simplicity. Memory usage is not that much of a
concern for uniforms.

Cleanup: DRW: Add draw_call_batching_flush for easier code understanding