We used to explicitly integrate the FCV upgrade/downgrade states inside the enum name.

The new system omits those details which makes communicating more difficult. The new raw values:

    kFullyDowngradedTo_5_0,
    kUpgradingFrom_5_0_To_5_1,
    kDowngradingFrom_5_1_To_5_0,
    kVersion_5_1,

The new fcv agnostic, synthetic values:

    static constexpr auto kLatest = FeatureCompatibilityVersion::kVersion_5_1;
    static constexpr auto kLastContinuous = FeatureCompatibilityVersion::kFullyDowngradedTo_5_0;
    static constexpr auto kLastLTS = FeatureCompatibilityVersion::kFullyDowngradedTo_5_0;

I propose changing:

• kVersion_5_1 to kFullyUpgradedTo_5_1
• kLatest to kFullyUpgradedToLatest
• kLastContinuous to kFullyDowngradedToLastContinuous
• kLastLTS to kFullyDowngradedToLastLTS