Add ConstraintLayout, RecyclerView and ViewModel lesson modules with code tabs

[MihaiCristianCondrea]

Motivation

• Expand the Android Studio lessons set by adding lessons demonstrating ConstraintLayout, RecyclerView, and ViewModel patterns with matching Java/XML syntax examples.
• Reuse existing UI patterns (SyntaxFabActivity + LessonCodeTabsActivity) so each lesson exposes Java and XML code in the same tabbed viewer used across the app.

Description

• Added three lesson packages and Activities: layouts/constraint/ConstraintLayoutActivity, lists/recyclerview/RecyclerViewActivity, and architecture/viewmodel/ViewModelActivity, each extending SyntaxFabActivity and wired to LessonCodeTabsActivity.createIntent(...) for Java/XML tabs.
• Implemented tab fragments to display code from raw assets (*TabCodeFragment and *TabLayoutFragment) and added the raw assets under res/raw following the text_<lesson>_java.txt / text_<lesson>_xml.txt naming pattern.
• Added supporting UI layouts and components: activity_constraint_layout.xml, activity_recycler_view.xml, activity_view_model.xml, item_recycler_view_lesson.xml, and a RecyclerViewPreviewAdapter for the RecyclerView preview.
• Registered new lessons in app/src/main/res/xml/preferences_android_studio.xml, added titles/summaries/strings in res/values/strings.xml, and declared the new Activities in AndroidManifest.xml.

Testing

• Ran ./gradlew test, which failed in this environment because the Android SDK location is not configured (missing ANDROID_HOME or local.properties sdk.dir).
• Validated XML well-formedness for modified/added XML files using a Python ET.parse check, which succeeded for the updated files.

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Codex Task