[templates] fix broken/wrong item template contents (#7366)

After working on #7349, I found some really odd behavior if you name
an Android layout, `my_cool_layout.xml`.

VS appears to generate:

    <?xml version="1.0" encoding="utf-8"?>
    <Linearmy_cool_layout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical"
        android:my_cool_layout_width="match_parent"
        android:my_cool_layout_height="match_parent">

    </Linearmy_cool_layout>

This is completely broken! It appears that anywhere the word `Layout`
was replaced with `my_cool_layout`. I also get the same behavior with
`dotnet new android-layout -n my_cool_layout`.

To solve this issue, I made the default name `Layout1`, so that
`<LinearLayout/>` and `android:layout_width`, are not replaced.

Now I get a `my_cool_layout.xml` with the contents:

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </LinearLayout>

Secondly, the `android-activity` template if you run:

    dotnet new android-activity -n MyActivity

It will generate:

    [Activity(Label = "@string/app_name", MainLauncher = true)]
    public class MyActivity : Activity

Let's replace the label with the name passed in, and remove
`MainLauncher=true`, so we instead get:

    [Activity(Label = "MyActivity")]
    public class MyActivity : Activity

I think this will prevent confusion with multiple app launchers, etc.

src/Microsoft.Android.Templates/android-activity/Activity1.cs

@@ -1,6 +1,6 @@
 namespace AndroidApp1;
 
-[Activity(Label = "@string/app_name", MainLauncher = true)]
+[Activity(Label = "Activity1")]
 public class Activity1 : Activity
 {
     protected override void OnCreate(Bundle? savedInstanceState)

src/Microsoft.Android.Templates/android-layout/.template.config/template.json

@@ -10,9 +10,9 @@
   },
   "identity": "Microsoft.Android.AndroidLayout",
   "shortName": "android-layout",
-  "sourceName": "Layout",
+  "sourceName": "Layout1",
   "primaryOutputs": [
-    { "path": "Layout.xml" }
+    { "path": "Layout1.xml" }
   ],
-  "defaultName": "Layout"
+  "defaultName": "Layout1"
 }