[templates] use copyOnly for certain files

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

src/Templates/src/templates/maui-blazor/.template.config/template.json

@@ -12,6 +12,13 @@
       "type": "solution"
     },
     "sourceName": "MauiApp1",
+    "sources": [
+      {
+        "source": "./",
+        "target": "./",
+        "copyOnly": [ "**/wwwroot/css/**", "**/*.svg", "**/*.ttf" ]
+      }
+    ],
     "preferNameDirectory": true,
     "primaryOutputs": [
       { "path": "MauiApp1/MauiApp1.csproj" },

src/Templates/src/templates/maui-mobile/.template.config/template.json

@@ -12,6 +12,13 @@
       "type": "solution"
     },
     "sourceName": "MauiApp1",
+    "sources": [
+      {
+        "source": "./",
+        "target": "./",
+        "copyOnly": [ "**/*.svg", "**/*.ttf" ]
+      }
+    ],
     "preferNameDirectory": true,
     "guids": [
       "07CD65EF-6238-4365-AF5D-F6D433967F48",