Fix multisite entry blueprint logic

[jasonvarga]

In #3786 the blueprint key was made to always be saved to the entry file to fix #3783.

In #4402, there were 2 cases where we were seeing the wrong blueprint being used:

1. When you go to the create form and immediately change sites - that's because the blueprint query param was not passed along.
2. When you change sites immediately after creating the first entry - that's because the wrong blueprint was saved to the localized entry. The blueprint() method was only looking at the blueprint yaml value on the origin entry. It wasn't taking into account when it was set as a property, which would be the case when localizing a freshly created entry.

Now the blueprint will only be saved to localized entries if it differs from the origin. 99% of the time it'll never differ - it doesn't really make sense. It'll only happen if you programmatically do it with $localization->blueprint('different')

Fixes #4402