Exclude fuchsia-sdk/sdk/.build-id from the builder cache archive (#187826)

The .build-id directory is created by the Fuchsia gen_build_defs.py
script which is run during gclient sync. It contains links to Fuchsia
SDK binaries in a directory structure that indexes the binaries by their
hashes.

The builder cache updater creates an archive of the source tree and its
dependencies. This archive does not need to include the .build-id tree.
Any necessary parts of .build-id will be written when each CI builder
does its own local run of gclient sync.

Currently the gen_build_defs.py script does not delete any of the
contents of .build-id when it updates .build-id for the current Fuchsia
SDK. That means that .build-id will continue to grow each time the tree
syncs to a new Fuchsia SDK, and all of these files were being added to
the builder cache archive. In a recent sample of the builder cache,
.build-id files were nearly 80% of the archive's contents.

engine/src/flutter/.ci.yaml

diff --git a/engine/src/flutter/.ci.yaml b/engine/src/flutter/.ci.yaml
index de2363f..f33e21a 100644
--- a/engine/src/flutter/.ci.yaml
+++ b/engine/src/flutter/.ci.yaml
@@ -81,6 +81,10 @@
           "builder",
           "git"
         ]
+      ignore_cache_paths: >-
+        [
+          "builder/engine/src/third_party/fuchsia-sdk/sdk/.build-id"
+        ]
       gclient_variables: >-
         {
           "download_emsdk": "true",
@@ -101,6 +105,10 @@
           "builder",
           "git"
         ]
+      ignore_cache_paths: >-
+        [
+          "builder/engine/src/third_party/fuchsia-sdk/sdk/.build-id"
+        ]
       gclient_variables: >-
         {
           "download_android_deps": "true",
@@ -122,6 +130,7 @@
         ]
       ignore_cache_paths: >-
         [
+          "builder/engine/src/third_party/fuchsia-sdk/sdk/.build-id",
           "builder/src/flutter/prebuilts/SDKs",
           "builder/src/flutter/prebuilts/Library"
         ]