Support Hybrid SDKs

[romtsn]

Description

Currently all our hybrid SDKs either recommend using SAGP or doing things their own way depending on the use-case. For example:

• React Native: Uploading source context and proguard mappings + custom script to upload sourcemaps
• Flutter: Uploading source context and proguard mappings
• Unity: Modifying Gradle scripts generated by the unity editor to apply the sdk dependencies, upload debug symbols, apply proguard rules
• KMP: configuring linker options to make SPM work and auto-installing kmp deps

Ideally we should eliminate those and provide first-class support for the Hybrid SDKs from the SAGP side. There should be subplugins for each hybrid SDK type (e.g. io.sentry.gradle.react-native or io.sentry.gradle.unity). The common functionality (like uploading debug symbols/proguard mappings) should be extracted into a common folder/module and shared between those subplugins. The new functionality should be built on top of that and support various gradle features such as configuration cache, isolated projects, build cache, task avoidance, etc.