Update blurhash for Kotlin library

[justin13888]

The existing Kotlin code has been unchanged since 5 years ago, however, existing Android tooling will not compile this code given how outdated versions are. It also written before Jetpack Compose was stabilized which has now become the standard.

This PR includes:

• Refactor of demo to use the latest Jetpack Compose setup
• Decoder library was refactored to use the new Kotlin Multiplatform structure with sourcesets. (The reason to include KMP dependencies is that blurhash shouldn't assume the decoder is just for Android clients. It would be helpful to have a consistent Kotlin implementation used across any Kotlin development, such as in a JVM server, Kotlin/Native, etc.)

Note: Prior to merging, there are some small non-blocking odd ends to finalize which were marked with a "TODO".