runtime(vim): Update base syntax, match generic functions

Match Vim9 generic functions, added in #17313.

closes: #17722

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

runtime/syntax/testdir/input/vim9_generic_functions.vim

@@ -0,0 +1,97 @@
+vim9script
+# Vim9 generic functions
+# VIM_TEST_SETUP highlight link vim9DefTypeParam Todo
+# VIM_TEST_SETUP let g:vimsyn_folding = "f"
+# VIM_TEST_SETUP setl fdc=2 fdl=99 fdm=syntax
+
+
+# :help generic-functions
+
+def MyFunc<T, A, B>(param1: T): T
+    var f: A
+    var x = param1
+    return x
+enddef
+
+MyFunc<number, string, list<number>>()
+
+
+def Flatten<T>(x: list<list<T>>): list<T>
+    var result: list<T> = []
+    for inner in x
+	result += inner
+    endfor
+    return result
+enddef
+
+echo Flatten<number>([[1, 2], [3]])
+
+
+class A
+    def Foo<X, Y>()
+    enddef
+endclass
+var a = A.new()
+a.Foo<number, string>()
+
+
+def MakeEcho<T>(): func(T): T
+    return (x: T): T => x
+enddef
+
+var EchoNumber = MakeEcho<number>()
+echo EchoNumber(123)
+
+var EchoString = MakeEcho<string>()
+echo EchoString('abc')
+
+# FIXME: add specific command handling
+# defcompile MyFunc<number, list<number>, dict<string>>
+
+# disassemble MyFunc<string, dict<string>>
+# disassemble MyFunc<number, list<blob>>
+
+
+# funcrefs
+
+var Foo = Bar<number>
+Execute(Bar<number>)
+
+var Foo = bar.Baz<string>
+Execute(bar.Baz<string>)
+
+class Foo
+  def _MethodA<T>(arg: T)
+    echo arg
+  enddef
+  def MethodB()
+    var F = this._MethodA<number>
+    F("text")
+  enddef
+endclass
+
+class Bar extends Foo
+  def MethodC()
+    var F = super._MethodA<number>
+    F("text")
+  enddef
+endclass
+
+
+# Issue: https://github.com/vim/vim/pull/17722#issuecomment-3075531052
+
+export def Id<U>(): func(U): U
+    return (X_: U) => X_
+enddef
+
+export def Const<U, V>(): func(U): func(V): U
+    return (X_: U) => (_: V) => X_
+enddef
+
+export def Flip<U, V, W>(): func(func(U): func(V): W): func(V): func(U): W
+    return (F_: func(U): func(V): W) => (Y_: V) => (X_: U) => F_(X_)(Y_)
+enddef
+
+echo Const<number, any>()(2)(null)
+    == Flip<number, any, number>()(Const<number, any>())(null)(2)
+