Expose `escapeGT` option in XLIFF package writer

[Chase Tingley]

We support the escapeGT option in the XLIFFWriter, but we don't expose it to the user through the XLIFFPackageWriter options. People occasionally grouse about our not escaping > in the XLIFF we produce, so this would give us an easy way to handle it.

[Chase Tingley]

Fix issue #702 - Add escapeGT option to XLIFFPackageWriter

→ <<cset acc092204ff4>>