TUI: rework background-color detection

- Like Vim, use set_option_value() followed by reset_option_was_set().
- Do not use set_string_default(), so the default is predictable.
  This affects `:set bg&`.
- Wait until end-of-startup (VimEnter) to handle the response. The
  response is racey anyways, so timing is irrelevant. This allows
  OptionSet to be triggered, unlike during startup.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/nvim/option.c b/src/nvim/option.c
index b85ec6dbcc..fc1fab834e 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -883,7 +883,7 @@ set_options_default (
 /// @param name The name of the option
 /// @param val The value of the option
 /// @param allocated If true, do not copy default as it was already allocated.
-void set_string_default(const char *name, char *val, bool allocated)
+static void set_string_default(const char *name, char *val, bool allocated)
   FUNC_ATTR_NONNULL_ALL
 {
   int opt_idx = findoption(name);