Do not capture `$set` event if user props have not changed

[marandaneto]

Description

https://github.com/PostHog/posthog-js/blob/c8c747a53c4768686542899631ebbe440ab39760/src/posthog-core.ts#L1589-L1593

Relates to #194

• Android/Flutter
• iOS/Flutter
• RN - requires this too

posthog-android/posthog/src/main/java/com/posthog/PostHog.kt

Lines 615 to 620 in b999daa

	capture(
	"\$set",
	distinctId = distinctId,
	userProperties = userProperties,
	userPropertiesSetOnce = userPropertiesSetOnce,
	)

this line should only be executed if userProperties or userPropertiesSetOnce have changed from previous calls.
we should cache userProperties and userPropertiesSetOnce in the cachePreferences to be able to compare