* Store checksums as a first-class piece of data in our persistence layer.

* Include the format version in the persistence checksum.

* Move symbol tree over to the checksym approach.

* Update sql persistence service to use checksums.

* Update tests.

* Fix wrapper.

* Remove projects.

* Add tests with checksums.

* Add more tests.

* Add test.

* Add comments.

* Simplify.

* Simplify.

* Revert.

* Revert.

* Revert.

* Add comment.

* Add comment.

* Add comment.

* Rev the checksum.

* Add comment.

* Add comment.

* Add comment.

* Add comment.

* Simplify.

* merge

* rename

* No allow checksym creation

* Rename

* cache strings

* simplify

* Remove optional params

* Update src/Workspaces/Core/Portable/FindSymbols/SyntaxTree/SyntaxTreeIndex_Persistence.cs
Co-Authored-By: NAndrew Harper <aharper@breuer.com>