feat(float): add winborder option (#31074)

Problem:
There is currently no global option to define the default border style for floating windows. This leads to repetitive code when developers need consistent styling across multiple floating windows.

Solution:
Introduce a global option winborder to specify the default border style for floating windows. When a floating window is created without explicitly specifying a border style, the value of the winborder option will be used. This simplifies configuration and ensures consistency in floating window appearance.

Co-authored-by: Gregory Anders <greg@gpanders.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/nvim/optionstr.c b/src/nvim/optionstr.c
index 3a6b4c9936..c3cdd6e804 100644
--- a/src/nvim/optionstr.c
+++ b/src/nvim/optionstr.c
@@ -2005,6 +2005,15 @@ const char *did_set_winhighlight(optset_T *args)
   return NULL;
 }
 
+/// The 'winborder' option is changed.
+const char *did_set_winborder(optset_T *args)
+{
+  if (opt_strings_flags(p_winbd, opt_winborder_values, NULL, true) != OK) {
+    return e_invarg;
+  }
+  return NULL;
+}
+
 int expand_set_winhighlight(optexpand_T *args, int *numMatches, char ***matches)
 {
   return expand_set_opt_generic(args, get_highlight_name, numMatches, matches);