fix(api): nvim_get_hl drops groups defined with link_global #38492

Problem: hlgroup2dict passes &ns_id to ns_get_hl twice. The first call
(link=true) sets *ns_hl = 0 when link_global is set, so the second call
and the sg_cleared guard both see ns_id == 0 and bail out. The group is
silently dropped from the result.

Solution: use a temporary copy of ns_id for each ns_get_hl call so the
original value is preserved.

runtime/lua/vim/_meta/api_keysets.lua

@@ -329,7 +329,7 @@ error('Cannot require a meta file')
 --- @field special? integer|string
 --- @field sp? integer|string
 --- @field link? integer|string
---- @field global_link? integer|string
+--- @field link_global? integer|string
 --- @field fallback? boolean
 --- @field blend? integer
 --- @field fg_indexed? boolean