Summary
SERVER-99351 introduced a new API for the FCV-gated feature flags that checks them against the operation FCV.
To ease the transition, existing feature flag checks were allowed to keep using the old API (specified by fcv_context_unaware: true idl parameter).
This ticket is for converting the featureFlagRankFusionFull to use the operation FCV-aware checks.

Background
This feature flag is non-trivial to convert to the new API because it checks feature flags inside the DocumentMetadataFields class which does not have an operation context available.

Goal
The goal of this ticket is to:

1. Switch featureFlagRankFusionFull to use the new FCVGatedFeatureFlag API by removing the fcv_context_unaware parameter from its idl specification.
2. Explore ways to make checking featureFlagRankFusionFull aware of the operation FCV by passing the VersionContext.

Note that the relience on the version context during checks can be bypassed by using one of the dummy values.
This approach will make the feature flag check fallback on the fcv snapshot parameter.
Please use this strategy only when strictly needed, as it might introduce inconsistent behavior if used incorrectly.