[templates] use copyOnly for certain files

[jonathanpeppers]

Description of Change

Context: dotnet/templating#3325
Context: https://github.com/dotnet/templating/wiki/Reference-for-template.json#content-manipulation

In current .NET 6 Preview 6 builds, there is an issue if a template
includes a binary file larger than ~8kb, it seems to get truncated when
dotnet new extracts the template.

A workaround is to use the copyOnly feature for binary files. Really,
we should be doing this anyway, because otherwise the templating system
considers replacing text in these binary files. It improves
performance to do this and would hopefully prevent a future bug of
random bytes getting replaced.

For .NET MAUI, the following files need copyOnly:

• wwwroot/css folder has several types of fonts inside
• .svg and .ttf files

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)
• Targets a single property for a single control (or intertwined few properties)
• Adds the property to the appropriate interface
• Avoids any changes not essential to the handler property
• Adds the mapping to the PropertyMapper in the handler
• Adds the mapping method to the Android, iOS, and Standard aspects of the handler
• Implements the actual property updates (usually in extension methods in the Platform section of Core)
• Tags ported renderer methods with [PortHandler]
• Adds an example of the property to the sample project (MainPage)
• Adds the property to the stub class
• Implements basic property tests in DeviceTests

Does this PR touch anything that might affect accessibility?

No

[jonathanpeppers]

@Eilon let me know if you see anything else in the maui-blazor template that needs this.

Related: dotnet/aspnetcore#33808

[mattleibow]

Looks like this got everything.