Copy static assets during BeforeBuild target to fix Visual Studio "rebuild" failures

[OzoneNZ]

Description

Fixes issue #11215 when using Rebuild option in Visual Studio/msbuild where every second rebuild would fail due to missing static asset files

Fixes #10760
Fixes #11215

msbuild output prior to this change:

1>Target _CopyOutOfDateSourceItemsToOutputDirectoryAlways:
1>  Microsoft.Common.CurrentVersion.targets(4996,5): error MSB3030: Could not copy the file "C:\Umbraco9Test\umbraco\config\appsettings-schema.json" because it was not found.
1>  Microsoft.Common.CurrentVersion.targets(4996,5): error MSB3030: Could not copy the file "C:\Umbraco9Test\umbraco\config\lang\cy.xml" because it was not found.
1>  Microsoft.Common.CurrentVersion.targets(4996,5): error MSB3030: Could not copy the file "C:\Umbraco9Test\umbraco\config\lang\en.xml" because it was not found.
1>  Microsoft.Common.CurrentVersion.targets(4996,5): error MSB3030: Could not copy the file "C:\Umbraco9Test\umbraco\config\lang\da.xml" because it was not found.

...

1>Done building target "_CopyOutOfDateSourceItemsToOutputDirectoryAlways" in project "Umbraco9Test.csproj" -- FAILED.
1>
1>Done building project "Umbraco9Test.csproj" -- FAILED.
1>
1>Build FAILED.

[umbrabot]

Hi there @OzoneNZ, thank you for this contribution! 👍

While we wait for one of the Core Collaborators team to have a look at your work, we wanted to let you know about that we have a checklist for some of the things we will consider during review:

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[p-m-j]

Works like a charm #h5yr!

[nathanwoulfe]

Am I right in assuming package devs should be making a similar change in .targets to avoid the same issue?

[p-m-j]

@nathanwoulfe I guess that depends on if the packages need to write files into the project directories for editing by their users.

We're hoping to move away from these msbuild hacks to immutable content in nuget packages and package developers should try to do so where possible also.

• If content files in the nupkg are only required when publishing/deploying, a nuspec with contentFiles will work great.
• If it's just adding static files to wwwroot then a razor class library is probably better (basically does the same as contentFiles but with a handy file provider for debugging).
• For immutable razor views it makes sense to embed them in the class library (or potentially use RCL's for distributing partials)
• What we're doing here is last resort and requires cleanup.

[bergmania]

Cherry picked to 9.0.1