Fix #3863 Changing logic regarding accepting url and text from share extension

[KacperWybranski]

Summary of Changes

This pull request fixes #3863
Logic changed from checking whether shared item is URL or text in NSItemProvider.loadItem to check it in Scheme initializer after accepting text data to app.

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()

Test Plan:

Verify that sharing url or text from other apps have not regressed

Screenshots:

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • release-notes/(include|exclude)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue is assigned to a milestone (should happen at merge time).

[KacperWybranski]

With this code, sharing text "https://www.apple.com apple" will cause searching with default search engine rather than opening first url in the string but it can be easily changed based on your opinion.

[iccub]

Thanks for this PR, let's wait with it until security review passes for our preview url scheme code, cc @jumde

[iccub]

this is now unblocked, will be delivered later, one release after your original search scheme pull request