DefaultUserPickerSearchService doesn't allow unlimited search

Issue Summary

Methods in DefaultUserPickerSearchService take UserSearchParams or maxResults value as a parameter to most of the methods.

The Java doc on UserSearchParams says:

     * @param maxResults           the maximum number of results to retrieve.  Use <code>null</code> for unlimited results.

However, inside DefaultUserPickerSearchService, there is an explicit check for the null value (and an explicit special value meaning unlimited results) that changes this value to MAX_MAX_RESULTS, which currently is equal to 1000:

    private int normalizeRidiculousUserPickerLimits(Integer resultLimit) {
        if (resultLimit == null || resultLimit == EntityQuery.ALL_RESULTS) {
            return MAX_MAX_RESULTS;
        } else {
            return resultLimit;
        }
    }

This means that the only way to obtain more than 1000 users from the search is to explicitly provide a big number as maxResults.
This approach is problematic though, as it can cause a high memory usage due to the way Lucene will handle this number - it will eagerly create an array of the passed-in size, so a caller providing MAX_INTEGER value to the method will user over 8GBs of memory.

Steps to Reproduce

N/A

Expected Results

DefaultUserPickerSearchService supports unlimited search, according to the Java doc.

Actual Results

DefaultUserPickerSearchService returns at most 1000 users when unlimited search is requested.

Workaround

A workaround is to explicitly set maxResults to a high number.
Note that this will use a lot of memory due to Lucene eagerly creating data structures, even if the final search will return 0 results.