Add top-right-serifed variants for Greek Lower Kappa (κ), for ss15.

[jmcwilliams403]

This is probably the last serif variant I will be adding for the time being.
I've also also added it to Latin K/k and Cyrillic К/к on principle.

This also adds an (internal-only) variant topLeftAndTopRightSerifed for letters like KDescender etc., whose bottom-right leg is occupied by some orthographic feature.

ABC.DEF.GHI.JKL.MNO.PQRS.TUV.WXYZ
abc.def.ghi.jkl.mno.pqrs.tuv.wxyz
!iIlL17|¦ ¢coO08BDQ $5SZ2zs ∂96µm
float il1[]={1-2/3.4,5+6=7/8%90};
1234567890 ,._-+= >< «¯-¬_» ~–÷+×
{*}[]()<>`+-=$/#_%^@\&|~?'" !,.;:
g9q¶ Þẞðþſß ΓΔΛαβγδηθικλμνξπτυφχψ
ЖЗКНРУЭЯавжзклмнруфчьыэя <= != ==

ss15 Upright:

Compared to IBM Plex Mono Upright (with IBM Plex Sans as a fallback):

ss15 Italic:

Compared to IBM Plex Mono Italic (again with IBM Plex Sans as a fallback):