[MLv2] Change expressions map into a vector of expressions (#31272)

src/metabase/lib/convert.cljc

src/metabase/lib/dev.cljc

src/metabase/lib/expression.cljc

src/metabase/lib/remove_replace.cljc

src/metabase/lib/schema.cljc

src/metabase/lib/schema/expression.cljc

src/metabase/lib/util.cljc

test/metabase/lib/aggregation_test.cljc

test/metabase/lib/convert_test.cljc

test/metabase/lib/expression_test.cljc

test/metabase/lib/remove_replace_test.cljc

test/metabase/lib/schema/expression/conditional_test.cljc

test/metabase/lib/schema_test.cljc

test/metabase/lib/stage_test.cljc