Native jni build (#5)

* Each native library is in its own jar. Got rid of cross compilation. The project is `secp256k1` and not `secp256k1-kmp`.

* Updated CI to use all 3 OS VMs

Co-authored-by: Salomon BRYS <salomon@kodein.net>

tests/build.gradle.kts

@@ -24,7 +24,7 @@ kotlin {
         }
         compilations["main"].dependencies {
             implementation(kotlin("stdlib-jdk8"))
-            implementation(project(":jni:jvm"))
+            implementation(project(":jni:jvm:all"))
         }
         compilations["test"].dependencies {
             implementation(kotlin("test-junit"))