[vm/aot] Separate out stream methods from the Elf class.

Introduce an internal StreamingWriteStream wrapper and use that instead.

Also add more ELF-defined constants and use those appropriately.

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-release-simarm_x64-try,vm-kernel-precomp-linux-product-x64-try
Change-Id: I2bd34ebac60e789aea82c8f064c59351e2c55dd3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149291
Reviewed-by: Clement Skau <cskau@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>

https://dart.googlesource.com/sdk/+/f89d930e38e2e5b5bc421e04cf37ba454ab7542c
diff --git a/commits.json b/commits.json
index 1f30c75..95e6670 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"c5d012900f7db0dc5dc9afb46f76d16b87915db0",
   "external/github.com/flutter/flutter":"a1636b6fef2ebe7840ba6dc1b3f9d77095ef3b45",
-  "sdk":"a2b5373eaac0fa36ac8fdda939b8fa26bd7d5633"
+  "sdk":"f89d930e38e2e5b5bc421e04cf37ba454ab7542c"
 }
\ No newline at end of file