Fix target name for flutter_patched_sdk so it doesn't conflict with...

Fix target name for flutter_patched_sdk so it doesn't conflict with patched_sdk target name, doesn't confuse ninja with depfile defined as .d (#3834)

BUILD.gn

@@ -7,7 +7,7 @@ group("flutter") {
 
   deps = [
     "//flutter/lib/snapshot:generate_snapshot_bin",
-    "//flutter/lib/snapshot:patched_sdk",
+    "//flutter/lib/snapshot:flutter_patched_sdk",
     "//flutter/sky",
   ]
 

lib/snapshot/BUILD.gn

@@ -313,7 +313,7 @@ template("generate_vm_patched_sdk") {
   }
 }
 
-generate_vm_patched_sdk("patched_sdk") {
+generate_vm_patched_sdk("flutter_patched_sdk") {
   libraries = [
     [
       "async",