CXX-3302 Update bsoncxx validation examples (CDRIVER-5710, CDRIVER-6017)

[eramongodb]

Followup to mongodb/mongo-c-driver#2026 which addressed CDRIVER-5710 and CDRIVER-6017. The changes in mongodb/mongo-c-driver@d184525 affect a couple assertions in the C++ Driver examples which demonstrate use of bsoncxx::v_noabi::validate() including the expected error offsets. Because the offsets are now changed/fixed, these examples need to be updated to run successfully.

This PR bumps the C Driver version to 2.0.2 for auto-downloads and EVG testing only. It does not bump the minimum required C Driver version for downstream users. We can also raise the minimum required C Driver version for downstream users if that is preferable (CXX-3302), but I do not think it is necessary at this time.

Alternatively we can defer applying this PR until the minimum required C Driver version for downstream users is bumped instead (e.g. when C Driver 2.1.0 is released).

Drive-by fix: also adds a missing import (followup to #1413) to address EVG config generator errors.

[kevinAlbs]

We can also raise the minimum required C Driver version for downstream users if that is preferable (CXX-3302), but I do not think it is necessary at this time.

I am open to debate, but I slightly prefer bumping the minimum required version to 2.0.2.

I see three distinct versions:

1. MONGOC_VERSION_MINIMUM is the tested version in CI.
2. MONGOC_DOWNLOAD_VERSION is the automatically downloaded version.
3. MONGOC_REQUIRED_VERSION is the required version.

I expect these do not strictly need to match, as is proposed in this PR. However, only bumping tested+downloaded means tests fail with the minimum required C driver. That may be unlikely to impact users, but bumping all to 2.0.2 avoids the possibility. The other benefit: upgrading to C++ driver 4.1.0 (with minimum C driver 2.0.2) is guaranteed to have the bug fix of CDRIVER-6017.

[eramongodb]

Done. Included a reference to CXX-3302 for tracking purposes.