exp/locale/collate: adjusted contraction trie to support Myanmar (Burmese),

exp/locale/collate: adjusted contraction trie to support Myanmar (Burmese),
which has a rather large contraction table. The value of the next state
offset now starts after the current block, instead of before.  This is
slightly less efficient (on extra addition per state change), but gives
some extra range for the offsets.
Also introduced constants for final (0) and noIndex (0xFF).
tables.go is updated in a separate CL.

R=r
CC=golang-dev
https://golang.org/cl/6346092