Merge remote-tracking branch 'origin/master' into AutoDetectLongPollingEnabledByDefault

Author: dconeybe

.changeset/dry-cats-lick.md

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+---
+'@firebase/app': patch
+---
+
+Make the error more helpful when `getApp()` is called before `initializeApp()`.

.changeset/funny-ways-carry.md

@@ -0,0 +1,5 @@
+---
+'@firebase/app': patch
+---
+
+Catch more heartbeat read/write errors.

.changeset/grumpy-bees-shake.md

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+---
+'@firebase/firestore': minor
+'firebase': minor
+---
+
+Added the ability to configure the long-polling hanging get request timeout using the new `idleHttpRequestTimeoutSeconds` setting