[vm] Increase alignment in the blob container format to 16k.

This accounts for the larger alignment required by mmap on ARM macOS.

Bug: #42534
Change-Id: Ie58732924d5a7287f2736696a6db0ddce7d308c1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153382
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Régis Crelier <regis@google.com>

runtime/bin/snapshot_utils.cc

@@ -22,7 +22,7 @@ namespace dart {
 namespace bin {
 
 static const int64_t kAppSnapshotHeaderSize = 5 * kInt64Size;
-static const int64_t kAppSnapshotPageSize = 4 * KB;
+static const int64_t kAppSnapshotPageSize = 16 * KB;
 
 class MappedAppSnapshot : public AppSnapshot {
  public: