configmgr: faster / simpler compare for keys.

A surprising amount of time is/was spent comparing keys in the
std::map red/black tree traversing nodes. Since we don't need
the data truly sorted, instead sort in length buckets. Kills
90k rtl_ustring_compare_withLength calls on startup, around
0.9% of headless start.

Change-Id: Ib23aff151ad50d56bbf2ba3e28882cc81898d9ec
sw: better encapsulate StyleSheet iterator's list.

Change-Id: I4fc06c739009a4754282854c4a0fce633213e50f
writerfilter: use XFastAttributes more efficiently.

Don't duplicate UTF8 as UCS2 before converting to integers.
Don't double convert every attribute, and allocate it twice.

Change-Id: Ibb15d703f011865dac8eb72f18408a5d62b60d96