v1: client_encryption (CXX-3237, CXX-3238)

[eramongodb]

Resolves CXX-3237 and CXX-3238 for the v1::client_encryption component.

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Similar to v_noabi::options::auto_encryption (#1551), v_noabi::options::client_encryption does not support direct v_noabi <-> v1 conversion due to the key vault client pointer field. However, similar to v_noabi::client (#1559), construction of v_noabi::client_encryption is still able to reuse the v1 implementation due to the pointer not being exposed post-construction. Therefore, v_noabi <-> v1 conversion is supported for the client_encryption class (but not its options class).

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Due to the comparative lack of option classes (whose v_noabi -> v1 conversions would constitute unconditional deep-copy performance overhead), many v_noabi functions were able to be implemented in terms of v1. This also helped to better highlight discrepancies in v1 and v_noabi behavior concerning optional return values, where v1 unconditionally returns BSON documents even when empty, whereas v_noabi returns a null optional instead:

// v_noabi
auto key_opt = ce.get_key();
if (key_opt) { use(*key_opt); }

// v1
auto key = ce.get_key();
if (!key.empty()) { use(key); }

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Following this PR, all former references to the scoped_bson_value helper have been replaced with bsoncxx::v1::types::value::internal::get_bson_value(). This helper can therefore be removed. The CSFLE-specific workaround for not-null BSON type strings is now implemented by the ensure_not_null_string() helper function.

[kevinAlbs]

LGTM!

[kevinAlbs]

Minor: can use the MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC and MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_RANDOM macros. Similar comment applies to v_noabi.