runtime(vim): Update base-syntax file, improve class, enum and interface highlighting

- Enable folding of class, enum and interface declarations.
- Highlight constructor names with the Function highlight group, like
  other special methods.
- Mark function definitions using special method names as errors.
- Highlight :type arguments.

fixes: #14393#issuecomment-2042796198.
closes: #13810

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

runtime/syntax/testdir/input/vim9_ex_commands.vim

@@ -93,7 +93,6 @@ vim9script
 :checktime
 :chistory
 :class
-:class
 :clast
 :clearjumps
 :clist
@@ -172,7 +171,6 @@ vim9script
 :elseif
 :emenu
 :endclass
-:endclass
 :enddef
 :endenum
 :endfor
@@ -385,8 +383,6 @@ vim9script
 :ptprevious
 :ptrewind
 :ptselect
-:public
-:public
 :put
 :pwd
 :py3
@@ -479,8 +475,6 @@ vim9script
 :startgreplace
 :startinsert
 :startreplace
-:static
-:static
 :stjump
 :stop
 :stopinsert
@@ -681,7 +675,6 @@ Foo() | checkpath
 Foo() | checktime
 Foo() | chistory
 Foo() | class
-Foo() | class
 Foo() | clast
 Foo() | clearjumps
 Foo() | clist
@@ -760,7 +753,6 @@ Foo() | else
 Foo() | elseif
 Foo() | emenu
 Foo() | endclass
-Foo() | endclass
 Foo() | enddef
 Foo() | endenum
 Foo() | endfor
@@ -972,8 +964,6 @@ Foo() | ptNext
 Foo() | ptprevious
 Foo() | ptrewind
 Foo() | ptselect
-Foo() | public
-Foo() | public
 Foo() | put
 Foo() | pwd
 Foo() | py3
@@ -1066,8 +1056,6 @@ Foo() | stag
 Foo() | startgreplace
 Foo() | startinsert
 Foo() | startreplace
-Foo() | static
-Foo() | static
 Foo() | stjump
 Foo() | stop
 Foo() | stopinsert