patch 8.2.2948: substitute() accepts a number but not a float expression

Problem:    Substitute() accepts a number but not a float expression.
Solution:   Also accept a float. (closes #8331)

src/testdir/test_substitute.vim

@@ -1,6 +1,7 @@
 " Tests for multi-line regexps with ":s".
 
 source shared.vim
+source check.vim
 
 func Test_multiline_subst()
   enew!
@@ -453,6 +454,13 @@ func Test_substitute_partial()
    call assert_fails("call substitute('123', '2', Replacer, 'g')", 'E118:')
 endfunc
 
+func Test_substitute_float()
+  CheckFeature float
+
+  call assert_equal('number 1.23', substitute('number ', '$', { -> 1.23 }, ''))
+  vim9 assert_equal('number 1.23', substitute('number ', '$', () => 1.23, ''))
+endfunc
+
 " Tests for *sub-replace-special* and *sub-replace-expression* on :substitute.
 
 " Execute a list of :substitute command tests

src/typval.c

@@ -462,8 +462,13 @@ tv_get_string_buf_chk_strict(typval_T *varp, char_u *buf, int strict)
 	    break;
 	case VAR_FLOAT:
 #ifdef FEAT_FLOAT
+	    if (strict)
+	    {
 		emsg(_(e_float_as_string));
 		break;
+	    }
+	    vim_snprintf((char *)buf, NUMBUFLEN, "%g", varp->vval.v_float);
+	    return buf;
 #endif
 	case VAR_STRING:
 	    if (varp->vval.v_string != NULL)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2948,
 /**/
     2947,
 /**/