Incorrect font shaping/layouting for Indic(-derived) scripts

[pluiedev]

Currently our rendering for Indic scripts (and scripts derived from/inspired by them) are quite broken, with overlapping characters (especially egregious in Tamil), incorrect vowel marks/diacritic placement, incorrect cursor placement, etc.

See previous discussions for each individual script:

• Devanagari: Devanagari support #2603
• Bengali: Bengali text's weird behavior in neovim #3912
• Thai: Ghostty unable to correctly render 🇹🇭 Thai text with vowels above/below the main character and tone marks, and would sometimes render overlapping characters #3753
• Tamil: Can ghostty handle other languages that are not monospaced #5085