Compute GPU projection matrix from camera's projection matrix.
In Unity, projection matrices follow OpenGL convention. However on some platforms they
have to be transformed a bit to match the native API requirements. Use this function
to calculate how the final projection matrix will be like. The value will match what
comes as UNITY_MATRIX_P matrix in a shader.
renderIntoTexture value should be set to true if you intend to render into a
RenderTexture with this projection matrix. On some platforms it affects how
the final matrix will look like.