Reproduction steps:
1. Open the attached project (bugreport.zip > lwrptest19).
2. Build and run it on an iOS device.

Actual behavior:
- ~390 MB RAM usage (2019.1 - 2019.3)
- About 30% increase
- Results may vary from 300 MB to 400 MB

Expected behavior:
- ~260 MB RAM usage (2018)

Memory usage increase:
* iOS (260 MB > 390 MB)
* macOS (87 MB > 87 MB)
* Android (44 MB > 52 MB) (VLNQA00103 Samsung Galaxy Note8 7.1.1 Exynos 9 Octa 8895 Mali-G71 OpenGL ES 3.2)

Reproduced with:
iPhone 6+ 12.1.4
iPad Air 11.0
iPhone 8 iOS 11.0
2019.1.4f1 (5.7.2)
2019.3.0a3 (5.7.2)

Not reproducible with:
2018.1.9f2(1.1.11)

Couldn't test reliably with:
2019.1.0a1
2018.3.14f1(4.10)

Notes:
* There are 2 attached projects: Lwrptest19 is for Unity 2019 (5.7.2 Package version); Lwrptest18 is for Unity 2018 (1.1.11 Package version).
* Moving project through Unity versions or changing Graphics APIs sometimes drops memory usage to ~50 MB. Originally reproduced on Metal, but swapping to GLES and then back to Metal reduces memory usage to ~50MB. Same results happen when changing LWRP to version 4.10. Couldn't reliably track down regression.

GPU Capture:
2018:
0 - render RenderTexture2
1 - render RenderTexture1. depth+stencil set to Store, but not used elsewhere.
2 - render shadow depth buffer for main camera
3 - depth pass for main camera. stencil set to Store, but not used elsewhere
4 - shadow map for main camera
5 - render main camera
6 - final blit

2019:
0 - render RenderTexture2
1 - render RenderTexture1. depth+stencil set to Store, but not used elsewhere.
2 - render shadow depth buffer for main camera
3 - depth pass for main camera
4 - clear shadow map for main camera
5 - unused MSAA resolve of cleared shadow map
6 - render shadow map for main camera
7 - MSAA resolve of shadow map
8 - render main camera 3D scene. depth+stencil set to Store, but not used elsewhere.
9 - MSAA resolve of main camera 3D scene
10 - render main camera 2D scene. depth+stencil set to Store, but not used elsewhere.
11 - final blit