UE5 layout changes

Content browser now hidden by default, opening tip is displayed showing you how to access it from the drawer. It can be permanently docked into the layout from there. Opening tip is never shown again
Placement browser is now closed by default
A UE4 classic layout has been added for those who want the placement browser and content browser docked by default

#jira UETOOL-2669

#ROBOMERGE-OWNER: matt.kuhlenschmidt
#ROBOMERGE-AUTHOR: matt.kuhlenschmidt
#ROBOMERGE-SOURCE: CL 15918688 in //UE5/Release-5.0-EarlyAccess/...
#ROBOMERGE-BOT: STARSHIP (Release-5.0-EarlyAccess -> Main) (v786-15839533)
#ROBOMERGE-CONFLICT from-shelf

[CL 15921147 by matt kuhlenschmidt in ue5-main branch]

Engine/Source/Editor/MainFrame/Private/MainFrameModule.cpp

@@ -195,7 +195,7 @@ void FMainFrameModule::CreateDefaultMainFrameAuxiliary(const bool bStartImmersiv
 			//     9.3. Etc
 			// 10. Push the new "DefaultLayout.ini" together with your new code.
 			// 11. Also update these instructions if you change the version number (e.g., from "UnrealEd_Layout_v1.4" to "UnrealEd_Layout_v1.5").
-			const FName LayoutName = TEXT("UnrealEd_Layout_v1.4");
+			const FName LayoutName = TEXT("UnrealEd_Layout_v1.5");
 			const TSharedRef<FTabManager::FLayout> DefaultLayout =
 				// We persist the positioning of the level editor and the content browser.
 				// The asset editors currently do not get saved.
@@ -213,17 +213,6 @@ void FMainFrameModule::CreateDefaultMainFrameAuxiliary(const bool bStartImmersiv
 					)
 				)
 				->AddArea
-				(
-					// content browser window
-					FTabManager::NewArea(WindowSize)
-					->Split
-					(
-						FTabManager::NewStack()
-						->SetSizeCoefficient(1.0f)
-						->AddTab("ContentBrowser1Tab", ETabState::ClosedTab)
-					)
-				)
-				->AddArea
 				(
 					// toolkits window
 					FTabManager::NewArea(WindowSize)