Fix GET_MANY in ra-data-json-server data provider returns too many results

[paradoxxxzero]

I think using the json-server like feature is not what we want here, since an id_like=2|33|444 will match 2, 33, 444 but also 23, 133 and so forth.
We could restrict the match with delimiters (^ and $) but since it supports multiple filters query, it would be simpler to use just that.

[fzaninotto]

Are you sure this works? I tested the /posts?id=[1,2] URL on JSONPlaceholder but it doesn't seem to filter the list.

[paradoxxxzero]

This is not /posts?id=[1,2] but /posts?id=1&id=2

> const {stringify} = require('query-string')
undefined
> stringify({id: [1, 2]})
'id=1&id=2'

[fzaninotto]

Gotcha, thanks for the explanation.

[fzaninotto]

And thanks for the PR!