How to reproduce:
1. Open the attached project from "DRSIssue.zip"
2. Open Scene "SampleScene"
3. In Game View options click "Load RenderDoc" and enter Play Mode
4. Launch RenderDoc and attach to an instance: Unity and capture a frame of the Game View
5. Double click the capture and navigate to "UIR.DrawChain -> UIR.ImmediateRender -> UniversalRenderPipeline.RenderSingleCamera -> ScriptableRenderer.Execute -> Render PostProcessing Effects -> StopNaNs"
6. In RenderDoc you can see the texture has been scaled down, right-click on the frame, click "Debug" and see in global values that _SourceTex_TexelSize variable has the original resolution

Actual result: Automatic shader variables like _MainTex_TexelSize are not reflecting DRS scaling of the RT set as the MainTex
Expected result: Automatic shader vars like _MainTex_TexelSize should reflect DRS scaling

Reproducible with: 10.5.0 - 13.0.0 (2020.3.20f1, 2021.1.25f1, 2021.2.0b16, 2022.1.0a13)
Couldn't test with: 7.7.1 (2019.4.31f1)

Note: Reproduction steps illustrated in the edit section