Introduce EditorWindowCapture class for Editor UI image comparison tests

Significantly improves the API in the Graphics Test Framework package and the Internal Editor API for capturing arbitrary Editor Windows.

- Adds new API to the Internal Editor Utility class to take snapshots of arbitrary windows instead of just SceneView windows
- Makes the older SceneView API obsolete
- Adds new API to the Graphics Test Framework to write the snapshot to a Texture2D for full compatibility with the current testing paradigm
- Refactors functionality for using this API on a SceneView window, leaving space for any other "special steps" done inside or outside the framework.
- Significantly improves the API usability and testability by moving away from IEnumerator setup and to an async setup instead.
- Updates the documentation around this functionality.

### Example captures

#### Scene view with no modifications

![SceneViewWindow_ImageIsNotNullOrEmpty](https://media.github.cds.internal.unity3d.com/user/2181/files/a5d944b3-021a-481e-b720-3708bae71e5a)

#### Scene view with all overlays disabled

![SceneViewWindow_ImageIsNotNullOrEmpty](https://media.github.cds.internal.unity3d.com/user/2181/files/7c79a8aa-10c9-4a5b-b281-491d0a3725be)

#### Scene view with most disabled + Debug Draw Mode

![SceneViewWindow_WithDebugDrawMode_ImageMatchesReference_BakedDirectionality_](https://media.github.cds.internal.unity3d.com/user/2181/files/27f23a76-ae59-4186-8257-898db5c34fa2)

#### Custom editor window

![CustomEditorWindowCaptureTest](https://media.github.cds.internal.unity3d.com/user/2181/files/067d9764-35ee-4d2d-a8ab-29637722db7d)

Author: ludeum

Tests/SRPTests/Projects/BatchRendererGroup_HDRP/Packages/manifest.json

@@ -56,7 +56,6 @@
     "com.unity.modules.xr": "1.0.0"
   },
   "testables": [
-    "com.unity.testframework.graphics",
     "com.unity.testing.xr"
   ],
   "useSatSolver": true,

Tests/SRPTests/Projects/BatchRendererGroup_URP/Packages/manifest.json

@@ -56,7 +56,6 @@
     "com.unity.modules.xr": "1.0.0"
   },
   "testables": [
-    "com.unity.testframework.graphics",
     "com.unity.testing.xr"
   ],
   "useSatSolver": true,

Tests/SRPTests/Projects/BuiltInGraphicsTest_Foundation/Packages/manifest.json

@@ -50,7 +50,6 @@
     "com.unity.modules.xr": "1.0.0"
   },
   "testables": [
-    "com.unity.testframework.graphics",
     "com.unity.testing.xr"
   ]
 }

Tests/SRPTests/Projects/BuiltInGraphicsTest_Lighting/Packages/manifest.json

@@ -50,7 +50,6 @@
     "com.unity.modules.xr": "1.0.0"
   },
   "testables": [
-    "com.unity.testframework.graphics",
     "com.unity.testing.xr"
   ]
 }

Tests/SRPTests/Projects/HDRP_DXR_Tests/Packages/manifest.json

@@ -50,7 +50,6 @@
   "testables": [
     "com.unity.render-pipelines.core",
     "com.unity.render-pipelines.high-definition",
-    "com.unity.testframework.graphics",
     "com.unity.testing.hdrp",
     "com.unity.testing.xr"
   ]

Tests/SRPTests/Projects/HDRP_RuntimeTests/Packages/manifest.json

@@ -50,7 +50,6 @@
   "testables": [
     "com.unity.render-pipelines.core",
     "com.unity.render-pipelines.high-definition",
-    "com.unity.testframework.graphics",
     "com.unity.testing.hdrp",
     "com.unity.testing.xr"
   ]

Tests/SRPTests/Projects/HDRP_Tests/Packages/manifest.json

@@ -55,7 +55,6 @@
   "testables": [
     "com.unity.render-pipelines.core",
     "com.unity.render-pipelines.high-definition",
-    "com.unity.testframework.graphics",
     "com.unity.testing.hdrp",
     "com.unity.testing.xr",
     "com.unity.shadergraph",

Tests/SRPTests/Projects/ShaderGraph/Packages/manifest.json

@@ -49,7 +49,6 @@
   },
   "disableProjectUpdate": true,
   "testables": [
-    "com.unity.shadergraph",
-    "com.unity.testframework.graphics"
+    "com.unity.shadergraph"
   ]
 }

Tests/SRPTests/Projects/ShaderGraphUniversalStereo/Packages/manifest.json

@@ -48,7 +48,6 @@
   "disableProjectUpdate": true,
   "testables": [
     "com.unity.render-pipelines.core",
-    "com.unity.render-pipelines.universal",
-    "com.unity.testframework.graphics"
+    "com.unity.render-pipelines.universal"
   ]
 }

Tests/SRPTests/Projects/UniversalGfxTestStereo/Packages/manifest.json

@@ -48,7 +48,6 @@
   "disableProjectUpdate": true,
   "testables": [
     "com.unity.render-pipelines.core",
-    "com.unity.render-pipelines.universal",
-    "com.unity.testframework.graphics"
+    "com.unity.render-pipelines.universal"
   ]
 }