Release/v6.4.0

[YYChen01988]

Enhancements

• FeatureFlags are now a copy-on-write structure, and so don't need to be defensive copied on a crashing thread #2005
• The default redactedKeys in ObjectJsonStreamer is now static and shared, reducing the overhead of some leaveBreadcrumb calls (those with complex metadata) #2008
• Allow Bugsnag.startSession to be called with automatic session tracking, and not have the first manual session be over written by the first automatic session. #2006

Bug fixes

• Refreshing the NDK symbol table is now protected by a soft-lock to avoid possible double-free conditions #2007

[bugsnagbot]

Android notifier sizes

Format	Size impact of Bugsnag (kB)	Size impact of Bugsnag when Minified (kB)
APK	1844.51	1668.58
arm64_v8a	626.95	450.82
armeabi_v7a	561.42	385.29
x86	704.75	524.53
x86_64	671.99	495.86

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