Added is_valid and post_dial_portion fields to DialerPhoneNumber.

These are frequently used attributes of numbers that we can compute once at parse-time.

Also did some general cleanup of DialerPhoneNumberUtil:

-Removed unused Future version of parse()
-Remove formatToValidE164 now that the new fields are available
-Inlined normalizeNumber()

Bug: 72563861
Test: existing
PiperOrigin-RevId: 183720128
Change-Id: I702dc265360e590439c5352c493ae8a858f36812