feat(extmarks): add virt_text_repeat_linebreak flag (#26625)

Problem:  Unable to predict which byte-offset to place virtual text to
          make it repeat visually in the wrapped part of a line.
Solution: Add a flag to nvim_buf_set_extmark() that causes virtual
          text to repeat in wrapped lines.

runtime/lua/vim/_meta/api_keysets.lua

@@ -251,6 +251,7 @@ error('Cannot require a meta file')
 --- @field virt_text_pos? string
 --- @field virt_text_win_col? integer
 --- @field virt_text_hide? boolean
+--- @field virt_text_repeat_linebreak? boolean
 --- @field hl_eol? boolean
 --- @field hl_mode? string
 --- @field invalidate? boolean