Fix src/main/res warnings due to AGP9

[cortinico]

Summary:

Fixes this warning that will break soon due to AGP9:

> Task :packages:react-native:ReactAndroid:generateDebugResources
Nested resources detected.
+ src/main/res
-- src/main/res/devsupport
-- src/main/res/shell
-- src/main/res/views/alert
-- src/main/res/views/modal
-- src/main/res/views/uimanager
-- src/main/res/views/view

Nested resources means you have layout like this:
res.srcDirs = [
    'src/main/res/',
    'src/main/res/category1'
]
However, you should use following structure instead:
res.srcDirs = [packages:rn-tester:android:app:de
    'src/main/res/common',
    'src/main/res/category1',
    'src/main/res/category2'
]
This Warning will be transformed into Error in version VERSION_9_0

Changelog:

[INTERNAL] -

Test Plan:

CI