patch 8.2.2784: Vim9: cannot use \=expr in :substitute

Problem:    Vim9: cannot use \=expr in :substitute.
Solution:   Compile the expression into instructions and execute them when
            invoked.
diff --git a/src/version.c b/src/version.c
index 9a2da2f..a43a2f4 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2784,
+/**/
     2783,
 /**/
     2782,