Once SPM-2880 delivers the FLEFindTextPayload, we will be able to finish the server rewrite work for $encStrStartsWith.

Goals for this task:

• Implement TextSearchPredicate::generateTags() for ExpressionEncStrStartsWith.
• Implement ExpressionEncStrStartsWith::evaluate() (this is our runtime evaluation during a column scan).
• Perform end to end testing of $encStrStartsWith, in supported read commands.
  • The end to end tests should go in a jstest under the fle2/ directory.
  • Look into making the end to end test a configurable test runner we can leverage for testing other expressions, and in all supported commands.

The code in the ExpressionEncTextSearch constructor will likely look like: 

 if (encryptedBinDataType) {
         auto tokens = ParsedFindTextSearchPayload(value);
        _evaluatorV2 = EncryptedPredicateEvaluatorV2(
            {ServerZerosEncryptionToken::deriveFrom(tokens.serverDataDerivedToken)});
    }  

While the lambda in evaluate_fle.cpp for evaluate(ExpressionEncStrStartsWith&) will likely look like:

 [&value](auto serverValue) {

            // extractMetadataBlocks should only be run once.
            tassert(10112800, "extractMetadataBlocks should only be run once by evaluate",
            !value);
             value.emplace(serverValue);
            std::vector<ConstDataRange> metadataBlocks;
            for (const auto& block : value->getPrefixMetadataBlocks()) {
                metadataBlocks.push_back(block.encryptedZeros);
            }
            return metadataBlocks;
        }