refactor: handle $0 according to the Zsh plugin standard (#10518)

For details and rationale, see:
https://zdharma-continuum.github.io/Zsh-100-Commits-Club/Zsh-Plugin-Standard.html

Closes #10518

plugins/colored-man-pages/colored-man-pages.plugin.zsh

@@ -16,6 +16,11 @@ less_termcap[se]="${reset_color}"
 less_termcap[us]="${fg_bold[green]}"
 less_termcap[ue]="${reset_color}"
 
+# Handle $0 according to the standard:
+# # https://zdharma-continuum.github.io/Zsh-100-Commits-Club/Zsh-Plugin-Standard.html
+0="${${ZERO:-${0:#$ZSH_ARGZERO}}:-${(%):-%N}}"
+0="${${(M)0:#/*}:-$PWD/$0}"
+
 # Absolute path to this file's directory.
 typeset __colored_man_pages_dir="${0:A:h}"