Improve documentation for nextPage() fuctions

Description

We should update the docs for the various method that support nextPage() function. This means:

• Anything returning (ISearchResults](https://developers.arcgis.com/arcgis-rest-js/api-reference/arcgis-rest-portal/ISearchResult/) so searchItems(), searchGroups(), searchUsers()
• findPlacesNearPoint() and findPlacesNearExtent()
• Add nextPage() support to queryFeatures() https://developers.arcgis.com/arcgis-rest-js/api-reference/arcgis-rest-feature-service/IQueryFeaturesResponse/

We should also document the pattern to paginate thorough resuts to get all results which generally looks like this:

function async getAllResults (response) {
 let allItems = lastResponse.results;

  // Keep getting the next page until there are no more pages.
  while (lastResponse.nextPage) {
    lastResponse = await lastResponse.nextPage();
    allItems = allItems.concat(lastResponse.results);
  }

  return allItems;
}

const allResults = await searchItems(options).then(getAllResults)

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