Add database runTransaction expect and js externals

Author: michaelprichardson

firebase-common/src/jsMain/kotlin/dev/gitlive/firebase/externals.kt

@@ -317,6 +317,11 @@ external object firebase {
             fun update(value: Any?): Promise<Unit>
             fun set(value: Any?): Promise<Unit>
             fun push(): ThenableReference
+            fun <T> runTransaction(
+                transactionUpdate: (currentData: T) -> T,
+                onComplete: (error: Error?, committed: Boolean, snapshot: DataSnapshot?) -> Unit,
+                applyLocally: Boolean?
+            ): Promise<T>
         }
 
         open class DataSnapshot {

firebase-database/src/commonMain/kotlin/dev/gitlive/firebase/database/database.kt

@@ -71,6 +71,8 @@ expect class DatabaseReference : Query {
     suspend fun <T> setValue(strategy: SerializationStrategy<T>, value: T, encodeDefaults: Boolean = true)
     suspend fun updateChildren(update: Map<String, Any?>, encodeDefaults: Boolean = true)
     suspend fun removeValue()
+
+    suspend fun <T> runTransaction(strategy: KSerializer<T>, transactionUpdate: (currentData: T) -> T): DataSnapshot
 }
 
 expect class DataSnapshot {