Fix some SMS encode issues.

1. Spanish SMS 71-160 chars not sent. This was because calculateLength
allowed for single-segment EMS encoding, while encodeUserDataPayload
did not.  For now, change calculateLength to match encodeUserDataPayload
(ie, fallback to UTF16 in this case).  (b/2224849)
2. Unicode value of N w/tilde was incorrect. (b/2224849)
3. Add '\' and '/' to the list of valid separators in CDMA SMS numeric
addresses. (b/2236527)