patch 8.2.1012: Vim9: cannot declare single character script variables

Problem:    Vim9: cannot declare single character script variables.
Solution:   Don't see "b:", "s:", etc. as namespace.  Fix item size of
            sn_var_vals.

src/scriptfile.c

@@ -1343,7 +1343,7 @@ do_source(
 
 	    // Allocate the local script variables to use for this script.
 	    new_script_vars(script_items.ga_len);
-	    ga_init2(&si->sn_var_vals, sizeof(typval_T), 10);
+	    ga_init2(&si->sn_var_vals, sizeof(svar_T), 10);
 	    ga_init2(&si->sn_imports, sizeof(imported_T), 10);
 	    ga_init2(&si->sn_type_list, sizeof(type_T), 10);
 # ifdef FEAT_PROFILE

src/testdir/test_vim9_script.vim

@@ -109,6 +109,41 @@ def Test_assignment()
   call CheckDefFailure(['v:errmsg += 123'], 'E1013:')
 enddef
 
+def Test_vim9_single_char_vars()
+  let lines =<< trim END
+      vim9script
+
+      " single character variable declarations work
+      let a: string
+      let b: number
+      let l: list<any>
+      let s: string
+      let t: number
+      let v: number
+      let w: number
+
+      " script-local variables can be used without s: prefix
+      a = 'script-a'
+      b = 111
+      l = [1, 2, 3]
+      s = 'script-s'
+      t = 222
+      v = 333
+      w = 444
+
+      assert_equal('script-a', a)
+      assert_equal(111, b)
+      assert_equal([1, 2, 3], l)
+      assert_equal('script-s', s)
+      assert_equal(222, t)
+      assert_equal(333, v)
+      assert_equal(444, w)
+  END
+  writefile(lines, 'Xsinglechar')
+  source Xsinglechar
+  delete('Xsinglechar')
+enddef
+
 def Test_assignment_list()
   let list1: list<bool> = [false, true, false]
   let list2: list<number> = [1, 2, 3]

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1012,
 /**/
     1011,
 /**/

src/vim9script.c

@@ -471,7 +471,7 @@ vim9_declare_scriptvar(exarg_T *eap, char_u *arg)
     }
 
     for (p = arg + 1; *p != NUL && eval_isnamec(*p); MB_PTR_ADV(p))
-	if (*p == ':' && p != arg + 1)
+	if (*p == ':' && (VIM_ISWHITE(p[1]) || p != arg + 1))
 	    break;
 
     if (*p != ':')