SI-8129 Make Object#== override Any#==

And the same for !=

If we tried to declare these signatures in non-fictional classes,
we would be chastised about collapsing into the "same signature after
erasure".

This will have an influence of typing, as the typechecking of
arguments is sensitive to overloading: if multiple variants are
feasible, the argument will be typechecked with a wildcard expected
type. So people inspecting the types of the arguments to `==` before
this change might have seen an interesting type for
`if (true) x else y`, but now the `If` will have type `Any`, as we
don't need to calculate the LUB.

I've left a TODO to note that we should really make `Any#{==, !=}`
non-final and include a final override in `AnyVal`. But I don't think
that is particularly urgent.
SI-8129 Crack the case of the curiously incoherent Context

 - Typer is created with Context.
 - Typer creates an Inferencer with said Context.
 - Typer mutates Typer#context after each import statement
 - Typer mutates its current Context (e.g to disable implicits.)
 - Typer asks a question of Inferencer
 - Inferencer thinks implicits that are fair game
 - Inferencer saves implicit ambiguities into the wrong Context.

Because of this bug, overload resolution in blocks or template
bodies for applications that follow an import have been
considering implicit coercions in the first try at static overload
resolution, and, in the rare case that it encounters an ambigous
implicit in the process, leaking an unpositioned ambiguout error.

This commit ensures coherency between `typer.context` and
`typer.infer.context` by making the latter delegate to the former.