Add hidden trailing `ɹ`s to the gb dictionaries

[AppAppWorks]

Currently misaki[en] cannot handle correctly "linking R" in British English, e.g.

# without linking r
"We are in" -> "wiː ɑː ˈɪn"
# with linking r, supposedly
"We are in" -> "wiː ɑːɹ  ˈɪn"

Therefore I suggest adding back the hidden trailing ɹ's to the gb dictionaries, e.g.

# with trailing r
"are" -> "ɑːɹ"
# instead of
"are" -> "ɑː"

Then, whenever a trailing ɹ is found not to be immediately followed by a vowel, such ɹ will be opportunistically removed. TokenContext has already been doing backpropagation of future vowels and to's, it seems trivial to add future initial vowels to the mix to facilitate this operation.