[analysis_server] Prepare server for handling multiple URI schemes

This is a slight refactor that should not change any behaviour extracted to make a future CL smaller. It:

1. replaces the previous `dartFiles` filter that was specifically for the `file://` scheme with a `List` that can be added to in future.
2. wraps calls to pathContext.fromUri() and pathContext.toUri() in all LSP server to go through a new class (`ClientUriConverter`) that will be extended to support mapping between to custom URI schemes (instead of `file:///`) for generated files.

Change-Id: Ie8eadcca3cfd708e4dfde07c22d411101cc9ca0b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/346540
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Phil Quitslund <pquitslund@google.com>

https://dart.googlesource.com/sdk/+/da07f7a3e2674c2a6caf66fc79a12c0a4828c01f

DEPS

diff --git a/DEPS b/DEPS
index 7431c8c..e4beff1 100644
--- a/DEPS
+++ b/DEPS
@@ -275,7 +275,7 @@
 
   'engine/src/flutter': Var('flutter_git') + '/mirrors/engine' + '@' + 'eab7bd3b099927edf0a360592e611968222f7ff7',
 
-  'engine/src/third_party/dart': Var('dart_git') + '/sdk' + '@' + '017749f2fe342b8e92f39eaf734f2c5daf596a51',
+  'engine/src/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'da07f7a3e2674c2a6caf66fc79a12c0a4828c01f',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + 'b9aba43b44a9f3d0c9956fbd82f26b8808d5d32c',
 

commits.json

diff --git a/commits.json b/commits.json
index c7cac37..73c40de 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "engine/src/flutter":"eab7bd3b099927edf0a360592e611968222f7ff7",
-  "engine/src/third_party/dart":"017749f2fe342b8e92f39eaf734f2c5daf596a51",
+  "engine/src/third_party/dart":"da07f7a3e2674c2a6caf66fc79a12c0a4828c01f",
   "flutter":"b9aba43b44a9f3d0c9956fbd82f26b8808d5d32c"
 }
\ No newline at end of file