ci: use local, vendored yarn in Windows CI jobs (#34384)

We keep a version of yarn in the repo, at
`third_party/github.com/yarnpkg/`. All CI jobs should use that version
for consistency (and easier updates).

Previously, the Windows jobs did not use the local version. They used
the version that came pre-installed on the docker image that we used.
This made it more difficult to update the yarn version (something that
we might want to do independently of updating other dependencies, such
as Node.js).

This commit fixes this by setting up the Windows CI jobs to also use the
local, vendored version of yarn.

PR Close #34384

.circleci/config.yml

@@ -154,6 +154,10 @@ commands:
       - custom_attach_workspace
       # Install Bazel pre-requisites that aren't in the preconfigured CircleCI Windows VM.
       - run: ./.circleci/windows-env.ps1
+      - run:
+          # Overwrite the yarn installed in the docker container with our own version.
+          name: Overwrite yarn with our own version
+          command: ./.circleci/windows-yarn-setup.ps1
       - run: node --version
       - run: yarn --version
       - restore_cache:

.circleci/windows-yarn-setup.ps1

@@ -0,0 +1,14 @@
+# Use our local, vendored yarn in the global `yarn` command.
+$globalYarnDir = "$HOME\AppData\Roaming\yarn"
+$localYarnPath = & ${Env:ProgramFiles}\nodejs\node.exe ".\.circleci\get-vendored-yarn-path.js"
+
+# Create a directory to put the yarn PowerShell script.
+New-Item -Path "$globalYarnDir" -ItemType "directory" >$null
+
+# Create the yarn PowerShell script (using the inferred path to the local yarn script).
+Get-Content -Path ".\.circleci\windows-yarn.ps1.template" |
+  %{$_ -replace "{{ LOCAL_YARN_PATH_PLACEHOLDER }}", "$localYarnPath"} |
+  Add-Content -Path "$globalYarnDir\yarn.ps1"
+
+# Add the directory containing the yarn PowerShell script to `PATH`.
+Add-Content -Path $profile -Value ('$Env:path = "{0};" + $Env:path' -f $globalYarnDir)

.circleci/windows-yarn.ps1.template

@@ -0,0 +1,15 @@
+$exe=""
+if ($PSVersionTable.PSVersion -lt "6.0" -or $IsWindows) {
+  # Fix case when both the Windows and Linux builds of Node
+  # are installed in the same directory
+  $exe=".exe"
+}
+$ret=0
+if (Test-Path "$basedir/node$exe") {
+  & "$basedir/node$exe"  "{{ LOCAL_YARN_PATH_PLACEHOLDER }}" $args
+  $ret=$LASTEXITCODE
+} else {
+  & "node$exe"  "{{ LOCAL_YARN_PATH_PLACEHOLDER }}" $args
+  $ret=$LASTEXITCODE
+}
+exit $ret