Resolves a system identifier (fragmentless URI reference) or a
public identifier into a new input source. It is typically used
when a URI reference is encountered in the original stream and
needs to be resolved (e.g. to support an external entity
reference, XInclude, xsl:include/import, document(), etc.).
The hint parameter is used to give a hint as to what the
resolution will be used for. It is generally used for security
checks for the repository.
If the ignoreErrors flag is set, an error during resolution
(such as "file not found") will result in None being returned,
rather than raising an exception.