Add support for FTS

[nirinchev]

Adds an optional positional argument to the @Indexed annotation that enables running TEXT queries:

@RealmModel()
class _Book {
  late String title;

  @Indexed(RealmIndexType.fullText)
  late String summary;
}

final books = realm.query<Book>("summary TEXT \$0", "fantasy novel")

Fixes #1248.

[nielsenko]

Assuming you are right about DateTime not being a valid primary key, which is odd given that it is indexable.

[coveralls]

Pull Request Test Coverage Report for Build 5187739159

• 30 of 32 (93.75%) changed or added relevant lines in 4 files are covered.
• 88 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.03%) to 89.251%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/src/realm_property.dart	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
lib/src/realm_class.dart	1	93.93%
lib/src/native/realm_core.dart	87	90.75%

Totals
Change from base Build 5123836006:	-0.03%
Covered Lines:	3147
Relevant Lines:	3526

---

💛 - Coveralls

[nirinchev]

The macOS test failure is a timeout of the tests after 45 minutes, while the Ubuntu 20 failure is the Realm.logger supports logging from multiple isolates test and it seems unrelated to these changes.

[blagoev]

Added some suggestions. And I think we should remove RealmIndexType.none. It adds very little value and makes the API weird and prone to runtime errors.