signed ints are only larger if sizeof is strictly greater.

Add int64_to_size_t_safe

MSVC errors on decltype

MSVC compile errors on the named operators

Co-authored-by: Kevin Albertson <kevin.albertson@10gen.com>

* Add snapshot-sessions data.

This commit adds data from CXX-2371, as described here:
https://jira.mongodb.org/browse/CXX-2371



* Add cmake support for unified session tests.

* Add slight informational improvements to runner's environment variable
lookup.

* remove unnecessary CAPTURE of test file contents

* fix distinct result

* pass session argument to count_documents operation

* pass session argument to runCommand, updateOne, listDatabases, listCollections

* support listIndexes

* fix writeConcern parsing

* use wc majority for inserting initialData

* apply clang-format

* Fixup for test; cannot check condition until another bug is patched.

* Respond to review comments.

Signed-off-by: Jesse Williamson <jesse.williamson@mongodb.com>

Co-authored-by: Kevin Albertson <kevin.albertson@mongodb.com>