CLSA-2026-1777313322 vim: Fix of 3 CVEs

CVE-2021-4173: fix double free in Vim9 nested :def function definition - CVE-2022-3352: fix use-after-free when SpellFileMissing autocmd deletes the current buffer during spell file loading - CVE-2022-2343: fix heap buffer overflow in inscompladdinfercase when completing a long line with...