The acquireCollection() path uses maps and vectors to general-case the least-likely cases of collection acquisition. In most cases, these containers contain one item, but we're paying the cost for the worst case.

Ideally, we would refactor this code to fast-path the single-collection cases, but since that's hard, we should just try to use cheaper containers.

Ideas:

• Replace std::vector in the acquisitionRequests with absl::InlinedVector, which optimizes for the case of a small number of elements. The constructor lets us pre-allocate the vector with a single element in the common case.
• Replace stdx::unordered_map in the CollectionAcquisitions (which uses absl::node_hash_map) with absl::flat_hash_map which is more memory-efficient.
• Replace std::list in TransactionResources to use absl::InlinedVector. It's not clear that we need linked-list semantics here.
• Replace ResolvedNamespaceOrViewAcquisitionRequestsMap with a absl::InlinedVector. In the most common case, this should only be 1 element. It's also not immediately obvious that we need this to have constant-time lookup, but it does appear to need to be sorted. If we need to sort this in the multi-collection case, it would probably be cheaper to use std::sort once we've made all of the acquisition requests, rather than maintain a full tree data structure.