feat(frontends/lean/parser_expr): 'namespaces' have precedence over 'using'
feat(frontends/lean/parser_expr): 'namespaces' have precedence over 'using'

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

codyroux/lean0.1,codyroux/lean0.1,codyroux/lean0.1,codyroux/lean0.1