Cross compilation support

Based on !37 (merged) and !40 (merged). Fixes #35 (closed).

• Add RustTarget handling all target-specific operations.
• Add BuiltInCargoProfile and CustomCargoProfile to customize Cargo profiles to use.
• Add CargoPackage handling all operations on the Cargo package manifest.
• Make BuildCrateTask depend on all Rust source files (even the ones of the dependencies cached in ~/.cargo)
• Calculate the list of RustTarget based on the project's target and sourceSet configuration.
• Add abstract task CargoTask which automatically tries to invoke cargo in the default installation path.
  • Make tasks inherit CargoTask
• Create multiple BuildCrateTasks based on the generated RustTargets.
  • Detect ABI filter from android {} block and create CargoBuildTasks accordingly
  • Detect native targets and generate CargoBuildTasks accordingly
• Create BuildCrateTask both for debug and release variants.
• Make Jar tasks depend on build tasks for libraries published via the maven-publish plugin
• Populate environment variables for each target
  • CC_aarch64-linux-android, CXX_aarch64-linux-android, etc., for Android
• Pre-build operations
  • Read environment variables from Xcode and select variants for macOS and iOS
• Post-build operations
  • Copy NDK libraries like libaaudio.so, ...
  • Copy resulting .so files to directories pointed by sourceSets.jniLibs on Android
  • Support both MinGW and MSVC on Windows (Does the current implementation correctly handle this? Kotlin/Native should not be able to link Rust static library targeting x86_64-pc-windows-msvc...)
  • Modify Dylib search paths (the ones found with otool -L) for macOS JVM (Also required for Android Compose Preview) Not required
• Add example multiplatform app
  • Android (Compose)
  • iOS & macOS (SwiftUI)
  • Windows
  • macOS (AppKit)
  • Linux (GTK 4)
  • Java Swing
• Support customized target name (e.g. jvm("desktop"))
• Add unit tests for the Gradle plugin features
• Automatically detect whether Rust toolchains are installed via rustup target list and install otherwise
• Configure CI/CD

Issues

• Kotlin/Native MinGW is not linkable to Rust MinGW (lld-link: warning: ignoring unknown argument: -exclude-symbols:___chkstk_ms)
• Changes in ndkLibraries don't copy the new libraries to the final build result, even though FindDynamicLibraryTask re-runs