patch 8.1.2177: Dart files are not recognized

Problem:    Dart files are not recognized.
Solution:   Add a filetype rule. (Eugene Ciurana, closes #5087)

runtime/filetype.vim

@@ -425,6 +425,9 @@ au BufNewFile,BufRead *.csp,*.fdr		setf csp
 au BufNewFile,BufRead *.pld			setf cupl
 au BufNewFile,BufRead *.si			setf cuplsim
 
+" Dart
+au BufRead,BufNewfile *.dart,*.drt		setf dart
+
 " Debian Control
 au BufNewFile,BufRead */debian/control		setf debcontrol
 au BufNewFile,BufRead control

src/testdir/test_filetype.vim

@@ -122,6 +122,7 @@ let s:filename_checks = {
     \ 'cvs': ['cvs123'],
     \ 'cvsrc': ['.cvsrc'],
     \ 'cynpp': ['file.cyn'],
+    \ 'dart': ['file.dart', 'file.drt'],
     \ 'datascript': ['file.ds'],
     \ 'dcd': ['file.dcd'],
     \ 'debcontrol': ['/debian/control'],

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2177,
 /**/
     2176,
 /**/