Android build fix

[syoyo]

This PR fixes the build for Android. Requirements: Android Studio Jellyfish(2023.3.1) + SDK API level 33(Android 13. Required version for Google Play as of May 2024) Tested on Pixel5a(Android 14)

Changes

                                                                                                                                                                                                                                                                                            * gradle version was too old and Android Studio cannot bootstrap the build, so bumped gradle version to 8

• Adding namespace in build.gradle is now mandatory
• android:exported="true" is now required when an application have intent-filter(AndroidManifest.xml)
• Some build fixes in source files for Android target. * It also fixes referencing a temporal variable of BoundingBox https://github.com/SaschaWillems/Vulkan-glTF-PBR/blob/66cd286a5f7cd57a6343b7e881b1e3454e11620f/base/VulkanglTFModel.cpp#L1170

[SaschaWillems]

Thank you for this PR. Very much appreciated 👍🏻

[syoyo]

Thanks!