tree-wide: take in all *our* JSON structures also decimal strings

tree-wide: take in all *our* JSON structures also decimal strings

Let's be friendly in what we accept: whenever we define a JSON
structure, let's also allow decimal strings where we want an integer.

This patch purely replaces JSON_VARIANT_UNSIGNED by
_JSON_VARIANT_TYPE_INVALID in the various JsonDispatch[] tables, so that
we'll happily accept any type in json_dispatch(), so that
json_dispatch_uint64() and related tools can do their thing.

This does not switch over OCI (as a JSON structure not defined by us).