feat(go): Create go_prompt_info to add Go version to theme prompts (#8924)

* Create go_prompt_info to add go version to prompts

* golang: move go_prompt_info to plugin, guard and quote output

Addresses review feedback: the prompt helper only belongs to Go
developers, so it moves out of lib/ (sourced for every shell) into
plugins/golang/golang.plugin.zsh. Adds a $+commands[go] guard so
users without Go installed don't spawn a process or see a stderr
error on every prompt render, quotes the version output the same
way the rvm/nvm helpers do so a % can't be read as a prompt escape,
and adds the dummy go_prompt_info stub to
lib/prompt_info_functions.zsh for themes that call it when the
plugin isn't loaded.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0193G8TyNqmNnv6v9HsVafGa

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

lib/prompt_info_functions.zsh

@@ -21,6 +21,7 @@ function chruby_prompt_info \
   azure_prompt_info \
   tf_prompt_info \
   conda_prompt_info \
+  go_prompt_info \
 {
   return 1
 }

plugins/golang/README.md

@@ -39,3 +39,18 @@ plugins=(... golang)
 | gov    | `go vet`          | Vet examines Go source code and reports suspicious constructs |
 | gove   | `go version`      | Prints Go version                                             |
 | gow    | `go work`         | Work provides access to operations on workspaces              |
+
+## Prompt
+
+This plugin provides the `go_prompt_info` function to add the installed Go
+version to your prompt.
+
+For example:
+```
+PROMPT="%~$ "
+RPROMPT='$(go_prompt_info)'
+```
+changes your prompt to:
+```
+~/go/project$ ▋                                                     1.22.3
+```

plugins/golang/golang.plugin.zsh

@@ -36,3 +36,12 @@ alias gotofx='go tool fix'
 alias gov='go vet'
 alias gove='go version'
 alias gow='go work'
+
+## prompt
+function go_prompt_info() {
+  (( $+commands[go] )) || return
+  local go_prompt
+  go_prompt=$(go version | awk '{ print substr($3, 3) }')
+  [[ -z "${go_prompt}" ]] && return
+  echo "${ZSH_THEME_GO_PROMPT_PREFIX}${go_prompt:gs/%/%%}${ZSH_THEME_GO_PROMPT_SUFFIX}"
+}