Steps:
1. Open attached project
2. Open SampleScene, hit play
3. On ProjectView, select the RenderTexture asset
4. On inspector, observe the content of RenderTexture

Expected: The scene content occupies the whole RenderTexture, as stated in docs https://docs.unity3d.com/ScriptReference/Camera-targetTexture.html
Actual: The scene content occupies only the top right quarter of the RenderTexture

Reproducible: 2019.3.0a10, 2019.2.0b9, 2019.1.8f1, 5.6.5p1
Reproducible: Win DX11 / Win DX12 / Win Vulkan <- they respect Camera rect, so they are wrong

Not reproducible: Mac Metal / Mac GLCore / Win GLCore