Add utility method for resolving a FragmentActivity from Context.

core/util/src/main/java/org/signal/core/util/ContextExtensions.kt

@@ -6,8 +6,38 @@
 package org.signal.core.util
 
 import android.app.DownloadManager
+import android.content.BroadcastReceiver
 import android.content.Context
+import android.content.ContextWrapper
+import androidx.fragment.app.FragmentActivity
 
 fun Context.getDownloadManager(): DownloadManager {
   return this.getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager
 }
+
+fun Context.safeUnregisterReceiver(receiver: BroadcastReceiver?) {
+  if (receiver == null) return
+
+  try {
+    unregisterReceiver(receiver)
+  } catch (_: IllegalArgumentException) {
+  }
+}
+
+/**
+ * Attempts to resolve a [FragmentActivity] from this context. Throws an [IllegalStateException] if none is found.
+ */
+fun Context.requireFragmentActivity(): FragmentActivity {
+  return resolveFragmentActivity() ?: throw IllegalStateException("Required FragmentActivity context, but found: ${javaClass.name} instead.")
+}
+
+/**
+ * Attempts to resolve a [FragmentActivity] from this context. Returns null for non-activity contexts.
+ */
+fun Context.resolveFragmentActivity(): FragmentActivity? {
+  return when (val context = this) {
+    is FragmentActivity -> context
+    is ContextWrapper -> context.baseContext.takeUnless { it === this }?.resolveFragmentActivity()
+    else -> null
+  }
+}