runtime(vim): Update base-syntax, improve enum highlighting

Match enum values and missing class keywords.

fixes: #15970

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/vim9_ex_enum_fold.vim

@@ -2,6 +2,8 @@ vim9script
 # Vim :enum command
 # VIM_TEST_SETUP let g:vimsyn_folding = 'ef'
 # VIM_TEST_SETUP setl fdc=2 fdl=99 fdm=syntax
+# VIM_TEST_SETUP hi link vim9EnumValue Todo
+
 
 interface Interface1
 endinterface
@@ -29,11 +31,20 @@ enum Enum4
 endenum
 
 enum Enum5 implements Interface1, Interface2
-    Value1,
-    Value2,
-    Value3
-    def Method1()
-      def Nested()
-      enddef
+  Value1,
+  Value2,
+  Value3
+  def Method1()
+    def Nested()
     enddef
+  enddef
 endenum
+
+enum Enum6
+      #\ comment
+      \ implements Interface1, Interface2
+  Value1,
+  Value2,
+  Value3
+endenum
+