Add check for java reserved works in AndroidResource items

[dellis1972]

Context #9461

Some users are seeing the following error from aapt2.

APT2258 invalid symbol name 'com.companyname.mauiapp1:drawable/import'.
C:\Users*User\AppData\Local\Temp\2kevcthb.kih\com\companyname\mauiapp1\R.java*"

This is because import is a java reserved word. The aapt2 code generator is not taking that into account (like we do for C# designer.cs). As a result we get this error. Its not very helpful.
So lets introduce a new error APT0004 which will explicitly check for java keywords in resource filenames.
This will allow users to know why their build is failing.

[dellis1972]

/azp run

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[jonpryor]

Draft commit message:

Context: /~https://github.com/dotnet/android/issues/9461

[Android Resource names become Java identifiers][0], so if you have
an image named `Resources/drawable/import.png`, *eventually* this
will become part of an `R.java` file with contents:

	/* partial */ class R {
	    public static class drawable {
	        public static final int import = 0xdeadbeef;
	    }
	}

at which point `javac` gets irate, because `import` is a Java keyword
and that's not a valid location for that keyword.

Other Android tooling also knows about and respects this limitation,
e.g. `aapt2`, which could report:

	…com\example\app\R.java: error APT2258: invalid symbol name 'com.example.app:drawable/import'.

This isn't something we can fix; Java keywords cannot be used as
Android Resource names.

What we *can* do is improve the UX, and explicitly call this out.

Introduce a new error `APT0004` error which will explicitly check for
Java keywords in resource filenames.  This will allow users to know
why their build is failing:

	error APT0004: Invalid file name: Filenames cannot use Java reserved words.

[0]: https://developer.android.com/guide/topics/resources/providing-resources#Accessing

[jonpryor]

@dellis1972: while it's good to capture the filename case, that's not the only place where Resource names can appear and become Java identifiers. Two more places that come to mind are:

• Layouts

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent">
    <Button android:id="@+id/import" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/hello" />
  </LinearLayout>

  The android:id="@+id/import" should cause things to break.

• Strings:

  <resources>
    <string name="import">lol</string>
  </resources>

Can we check for these other occurrences as well? Should that be done as part of this PR, or separately?

[dellis1972]

@dellis1972: while it's good to capture the filename case, that's not the only place where Resource names can appear and become Java identifiers. Two more places that come to mind are:

• Layouts

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent">
    <Button android:id="@+id/import" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/hello" />
  </LinearLayout>
  

  The android:id="@+id/import" should cause things to break.

• Strings:

  <resources>
    <string name="import">lol</string>
  </resources>
  

Can we check for these other occurrences as well? Should that be done as part of this PR, or separately?

Lets do this in a new PR. The current task does not process the actual files. Plus we might need to take into account custom classes which happen later in the build system.