feat(marks): virtual lines support horizontal scrolling (#32497)

Add a new field `virt_lines_overflow` that enables horizontal scrolling
for virtual lines when set to "scroll".

runtime/lua/vim/_meta/api_keysets.lua

@@ -258,6 +258,7 @@ error('Cannot require a meta file')
 --- @field virt_lines? any[]
 --- @field virt_lines_above? boolean
 --- @field virt_lines_leftcol? boolean
+--- @field virt_lines_overflow? string
 --- @field strict? boolean
 --- @field sign_text? string
 --- @field sign_hl_group? integer|string