ensure all `isequal` methods to be inferred to return `Bool` (#49800)
This would help inference on `Core.Compiler.return_type(isequal, tt)`
when `tt` is not well inferred (e.g. `tt` is inferred to `Tuple{Any,Any}`).
(although JuliaLang/julia#46810 may disable this `Core.Compiler.return_type`
improvement for good reasons).
Anyway, it is explicitly stated in the documentation that the `isequal`
method should always return a value of `Bool`. So, not only does this
annotation assist inference, it also serves to ensure the correctness of
our code base, and therefore should be beneficial. We may need to take
similar measures for `isless` and `isgreater` (in separate PRs).
julia
dfbcc45f - ensure all `isequal` methods to be inferred to return `Bool` (#49800)
