Converting `tei:interleave` to `rng:interleave` for #2154

[trishaoconnor]

In order to implement TEIC/TEI#2154, we need proper processing in place for <tei:interleave> (which likely produces <rng:interleave>). The processing for <tei:interleave> will replace of the current process for <tei:sequence preserveOrder="false">.

[sydb]

This issue is address by #633. (Which was written to address #627, but since it required typing only ~30 extra characters to address this issue at the same time …) If & when that PR is merged into dev, I suspect this issue can just be closed.

[joeytakeda]

PR #633 adds handling for the (currently non-existent) tei:interleave element. However, we should wait until said element is created (per TEIC/TEI#2154) and we can actually test that it works before closing