Convert all known tri-compares that return an int to return std::strong_ordering.
Returning an int is dangerous since the caller can treat it as a bool, and indeed
this series uncovered a minor bug (#9103).
Test: unit (dev)
Fixes#1449Closes#9106
* github.com:scylladb/scylla:
treewide: remove redundant "x <=> 0" compares
test: mutation_test: convert internal tri-compare to std::strong_ordering
utils: int_range: change to std::strong_ordering
test: change some internal comparators to std::strong_ordering
utils: big_decimal: change to std::strong_ordering
utils: fragment_range: change to std::strong_ordering
atomic_cell: change compare_atomic_cell_for_merge() to std::strong_ordering
types: drop scaffolding erected around lexicographical_tri_compare
sstables: keys: change to std::strong_ordering internally
bytes: compare_unsigned(): change to std::strong_ordering
uuid: change comparators to std::strong_ordering
types: convert abstract_type::compare and related to std::strong_ordering
types: reduce boilerplate when comparing empty value
serialized_tri_compare: change to std::strong_ordering
compound_compat: change to std::strong-ordering
types: change lexicographical_tri_compare, prefix_equality_tri_compare to std::strong_ordering
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