feat(async)!: implement async prompt API and apply to git prompt (#12257)

BREAKING CHANGE: the `git_prompt_info` prompt function has been
reworked by default to use the new async prompt feature. If you're
experiencing issues see #12257.

Co-authored-by: Carlo Sala <carlosalag@protonmail.com>

lib/git.zsh

@@ -9,14 +9,18 @@ function __git_prompt_git() {
   GIT_OPTIONAL_LOCKS=0 command git "$@"
 }
 
-function git_prompt_info() {
+function _omz_git_prompt_status() {
   # If we are on a folder not tracked by git, get out.
   # Otherwise, check for hide-info at global and local repository level
   if ! __git_prompt_git rev-parse --git-dir &> /dev/null \
-     || [[ "$(__git_prompt_git config --get oh-my-zsh.hide-info 2>/dev/null)" == 1 ]]; then
+    || [[ "$(__git_prompt_git config --get oh-my-zsh.hide-info 2>/dev/null)" == 1 ]]; then
     return 0
   fi
 
+  # Get either:
+  # - the current branch name
+  # - the tag name if we are on a tag
+  # - the short SHA of the current commit
   local ref
   ref=$(__git_prompt_git symbolic-ref --short HEAD 2> /dev/null) \
   || ref=$(__git_prompt_git describe --tags --exact-match HEAD 2> /dev/null) \
@@ -33,6 +37,20 @@ function git_prompt_info() {
   echo "${ZSH_THEME_GIT_PROMPT_PREFIX}${ref:gs/%/%%}${upstream:gs/%/%%}$(parse_git_dirty)${ZSH_THEME_GIT_PROMPT_SUFFIX}"
 }
 
+# Enable async prompt by default unless the setting is at false / no
+if zstyle -T ':omz:alpha:lib:git' async-prompt; then
+  function git_prompt_info() {
+    _omz_register_handler _omz_git_prompt_status
+    if [[ -n "$_OMZ_ASYNC_OUTPUT[_omz_git_prompt_status]" ]]; then
+      echo -n "$_OMZ_ASYNC_OUTPUT[_omz_git_prompt_status]"
+    fi
+  }
+else
+  function git_prompt_info() {
+    _omz_git_prompt_status
+  }
+fi
+
 # Checks if working tree is dirty
 function parse_git_dirty() {
   local STATUS