Add contextual handling for narrow base + subscript –Ra in Kannada

[tiroj]

Problem: subscript –Ra applied to narrow base letters in Kannada results in collisions with preceding subscripts, e.g.

One way to solve this would be with a contextual narrow variant of subscript –Ra in GSUB, but this would be dependent on rclt cross-cluster support if we didn’t want the narrow subscript to always be used with the narrow bases.

Another solution is to add contextual spacing adjustment to the left side of the base in such situations. This has the benefit of working everywhere, but is a bit more complex and produces a gap within words (not uncommon in Kannada).