[clangd] Make categorical features 64 bit in DecisionForest Model.

CodeCompletionContext::Kind has 36 Kinds. The completion model used to
support categorical features of 32 cardinality.
Due to this clangd tests were failing asan tests due to overflow.

This patch makes the completion model support 64 cardinality of
categorical features by storing ENUM Features as uint64_t instead of
uint32_t.

Verified that this fixes the asan failures.

Latency: 6.7ms (old) VS 6.8ms (new) per 1000 predictions.

Differential Revision: https://reviews.llvm.org/D97770