vim-patch:partial:9.2.0573: Vim9: missing EX_WHOLE on some block keywords (#40071)

Problem:  Several Vim9 keywords lack EX_WHOLE and can be shortened in
          Vim9 script, inconsistent with endif/enddef/endfor/endwhile/
          endtry which already have it.  The error from :endd in a
          nested function also hardcodes "enddef" instead of reporting
          what the user typed.  fullcommand("ho") returns "horizontal"
          even though :ho is below the documented 3-char minimum.
Solution: Add EX_WHOLE to :class, :def, :endclass, :endinterface,
          :endenum, :public and :static.  In get_function_body() pass
          the user-typed command to the error message.  Force :ho to
          CMD_SIZE in find_ex_command() so fullcommand() reflects the
          modifier minimum.  Extend tests and documentation accordingly
          (Peter Kenny).

fixes:  vim/vim#20032
closes: vim/vim#20191

38d9a16eba

Co-authored-by: Peter Kenny <github.com@k1w1.cyou>

src/nvim/eval.lua

@@ -3230,9 +3230,16 @@ M.funcs = {
       Returns an empty string if a command doesn't exist or if it's
       ambiguous (for user-defined commands).
 
-      For example `fullcommand('s')`, `fullcommand('sub')`,
-      `fullcommand(':%substitute')` all return "substitute".
-
+      Note: Command validation is not performed.  Results depend on
+      Vim's internal command-specific identification rules.
+      Examples:
+      >vim
+        echo [fullcommand('s')]		|" ['substitute']
+        echo [fullcommand('sub')]		|" ['substitute']
+        echo [fullcommand(': mark word')]	|" ['mark']
+        echo [fullcommand(': markword')]	|" ['']
+        echo [fullcommand('en')]		|" ['endif']
+      <
     ]=],
     name = 'fullcommand',
     params = { { 'name', 'string' } },