[analysis_server] Fix line endings in snippets

This removes `useLineEndingsForPlatform=false` from the Snippets tests and updates them to use a shared method that correctly handles normalization of the `expected` result.

It turned out that we had bugs here, with the correct line endings not being used, so it also fixes that by passing `eol` to the `ChangeBuilder`s created by the snippet producers.

Progress towards https://github.com/dart-lang/sdk/issues/60234

Change-Id: I851fee987dda52f329d110878e10593cbced8c6c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/433780
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

https://dart.googlesource.com/sdk/+/f717a0ef7ea76440f8c67ccf25c8d54cca76c25a

DEPS

diff --git a/DEPS b/DEPS
index 7ad2ddc..77a4b70 100644
--- a/DEPS
+++ b/DEPS
@@ -235,7 +235,7 @@
 ]
 
 deps = {
-  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '14889cc06d62f7c2941248960704db15be31bff0',
+  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'f717a0ef7ea76440f8c67ccf25c8d54cca76c25a',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '4067b941d8eb3b0d9c47e67cd4b3eb5cb44d9dfb',
 

commits.json

diff --git a/commits.json b/commits.json
index ffd2ac5..5ccf8e3 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
   "flutter":"4067b941d8eb3b0d9c47e67cd4b3eb5cb44d9dfb",
-  "flutter/engine/src/flutter/third_party/dart":"14889cc06d62f7c2941248960704db15be31bff0"
+  "flutter/engine/src/flutter/third_party/dart":"f717a0ef7ea76440f8c67ccf25c8d54cca76c25a"
 }
\ No newline at end of file