Bias octahedral tangent y axis to avoid errors around 0

[clayjohn]

Fixes: #71571

This also fixes the simplified MRP in #71221 (comment) but I am unsure if it fixes the OP of #71221

In 3.x we applied a small bias to the tangent y axis while it was in the range [0, 1] to avoid discontinuities around 0

godot/servers/visual_server.cpp

Lines 369 to 375 in 8104416

	Vector2 VisualServer::tangent_to_oct(const Vector3 v, const float sign, const bool high_precision) {
	float bias = high_precision ? 1.0f / 32767 : 1.0f / 127;
	Vector2 res = norm_to_oct(v);
	res.y = res.y * 0.5f + 0.5f;
	res.y = MAX(res.y, bias) * SGN(sign);
	return res;
	}

In 4.0 the code is a little different because the output from octahedron_encode is already in [0,1] space.

Somehow we missed the bias when converting to 4.0, but it is still needed in some very rare cases.

Big thanks to @stoofin who narrowed the issue down to tangents with y-values very close to 0

[akien-mga]

Thanks!

[clayjohn]

I'm still having this issue with 4.0.2

Have you tried reimporting your asset?