Depth buffer and SimpleRenderTarget

[sellendk]

Describe the bug
In all of the glyph shaders in the GlyphRenderer, there is a problem regarding the depth buffer. Currently, the depth gets written to a color attachment:

depth_out = ((depth / depth_w) + 1.0) * 0.5;

But, this has no impact on the depth buffer that gets returned by the SimpleRenderTarget, since the SimpleRenderTarget returns the actual DB:

ct->setData(m_GBuffer->getDepthStencil(), m_version);

In case of the box glyph, this lucks out, but for all the other glyphs and all other possible renderers that are connected, the DB is probably wrong.

Expected behavior
If the depth gets calculated 'by hand', it needs to be written to the depth buffer:

float final_depth = ((depth / depth_w) + 1.0) * 0.5;
gl_FragDepth = final_depth; // depth buffer
depth_out = final_depth;    // color attachment. can be thrown out, if not used otherwise