Fix wording in documentation

[James-Mart]

Fixes some errors in the docs.

Also changed the wording in locals.rs to improve its consistency with the wording in the corresponding function docs in globals.rs and memories.rs.

[James-Mart]

Somehow I doubt that my updates to the docs are responsible for the CI failures:

failures:

---- tests_round_trip_elem_segments_1_wat stdout ----
thread 'tests_round_trip_elem_segments_1_wat' panicked at crates/tests-utils/src/lib.rs:107:23:
got an error: unexpected token, expected one of: `funcref`, `externref`, `exnref`, `anyref`, `eqref`, `structref`, `arrayref`, `i31ref`, `nullfuncref`, `nullexternref`, `nullref`, left paren
     --> tests/round_trip/elem-segments-1.wat:2:12
      |
    2 |   (table 1 anyfunc)
      |            ^