[ci] Bring up LUCI Linux custom package tests (flutter#4382)

Adds LUCI version of Linux custom package tests.

Removes the custom tests for `cross_file` and `google_identity_services_web` since they only existed to run unit tests in browser mode, which is [now standard for all packages that can be run that way](flutter/packages#4378).

Part of flutter#114373

Author: stuartmorgan-g

.ci.yaml

@@ -214,6 +214,40 @@ targets:
       channel: stable
       version_file: flutter_stable.version
 
+  - name: Linux_android custom_package_tests master
+    bringup: true # New target
+    recipe: packages/packages
+    timeout: 30
+    properties:
+      add_recipes_cq: "true"
+      version_file: flutter_master.version
+      target_file: linux_custom_package_tests.yaml
+      cores: "32"
+      # Pigeon tests need Andoid deps (thus the Linux_android base) and
+      # clang-format.
+      dependencies: >-
+        [
+          {"dependency": "clang", "version": "git_revision:5d5aba78dbbee75508f01bcaa69aedb2ab79065a"}
+        ]
+      channel: master
+
+  - name: Linux_android custom_package_tests stable
+    bringup: true # New target
+    recipe: packages/packages
+    timeout: 30
+    properties:
+      add_recipes_cq: "true"
+      version_file: flutter_stable.version
+      target_file: linux_custom_package_tests.yaml
+      cores: "32"
+      # Pigeon tests need Android deps (thus the Linux_android base) and
+      # clang-format.
+      dependencies: >-
+        [
+          {"dependency": "clang", "version": "git_revision:5d5aba78dbbee75508f01bcaa69aedb2ab79065a"}
+        ]
+      channel: stable
+
   ### Android tasks ###
   - name: Linux_android android_build_all_packages master
     recipe: packages/packages

.ci/scripts/custom_package_tests.sh

@@ -4,11 +4,5 @@
 # found in the LICENSE file.
 set -e
 
-# Exclusions
-#
-# script/configs/linux_only_custom_test.yaml
-#   Custom tests need Chrome. (They run in linux-custom_package_tests)
-
 dart ./script/tool/bin/flutter_plugin_tools.dart custom-test \
-   --packages-for-branch --log-timing \
-   --exclude=script/configs/linux_only_custom_test.yaml
+   --packages-for-branch --log-timing

.ci/targets/linux_custom_package_tests.yaml

@@ -0,0 +1,6 @@
+tasks:
+  - name: prepare tool
+    script: .ci/scripts/prepare_tool.sh
+  - name: custom tests
+    script: script/tool_runner.sh
+    args: ["custom-test"]