[indic] Support more extended Devanagari tone marks

Also adjust U+0953,0954 handling.
[indic] Allow up to three tone marks

According to Roozbeh, there are valid combinations in Unicode
proposals for up to three.  Previously we were allowing up to two.
[indic] Recategorize U+A8E0..A8F1 as OT_VD

Up to two of them come after all OT_A characters.
[indic] Treat U+1CE1 as a tone-mark too

It's spacing, but otherwise the same as the other ones.
[indic] Support U+1CF5,1CF6
Minor
[indic] Support U+1CE2..U+1CE8
[indic] Support U+1CF2,U+1CF3