refactor: start migrating some signatures to Kotlin

src/main/kotlin/app/revanced/signatures/SignatureSupplier.kt

@@ -0,0 +1,7 @@
+package app.revanced.signatures
+
+import app.revanced.patcher.signature.MethodSignature
+
+interface SignatureSupplier {
+    fun get(): MethodSignature
+}