Add spell check tools to eng/common

eng/common/pipelines/templates/steps/check-spelling.yml

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+# Checks spelling of files that changed between the current state of the repo
+# and some ref (branch, tag, etc.) or commit hash. Only runs on PRs.
+# ContinueOnError   - true: Pipeline warns on spelling error 
+#                     false: Pipeline fails on spelling error
+# TargetBranch      - Target ref (e.g. master) to compare to create file change
+#                     list.
+# CspellConfigPath  - Path to cspell.json config location
+
+parameters:
+  ContinueOnError: true
+  TargetBranch: $(System.PullRequest.TargetBranch)
+  SourceBranch: HEAD
+  CspellConfigPath: ./.vscode/cspell.json
+
+steps:
+  - ${{ if eq(variables['Build.Reason'], 'PullRequest') }}:
+    - task: PowerShell@2
+      displayName: Check spelling (cspell)
+      continueOnError: ${{ parameters.ContinueOnError }}
+      inputs: 
+        targetType: filePath
+        filePath: eng/common/scripts/check-spelling-in-changed-files.ps1
+        arguments: >- 
+          -TargetBranch "origin/$("${{ parameters.TargetBranch }}" -replace "refs/heads/")"
+          -SourceBranch ${{ parameters.SourceBranch }}
+          -CspellConfigPath ${{ parameters.CspellConfigPath }}
+        pwsh: true

eng/common/scripts/check-spelling-in-changed-files.ps1

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+[CmdletBinding()]
+Param (
+    [Parameter()]
+    [string] $TargetBranch,
+
+    [Parameter()]
+    [string] $SourceBranch,
+
+    [Parameter()]
+    [ValidateNotNullOrEmpty()]
+    [string] $CspellConfigPath = "./.vscode/cspell.json"
+)
+
+$ErrorActionPreference = "Continue"
+. $PSScriptRoot/logging.ps1
+
+if ((Get-Command git | Measure-Object).Count -eq 0) { 
+    LogError "Could not locate git. Install git https://git-scm.com/downloads"
+    exit 1
+}
+
+if ((Get-Command npx | Measure-Object).Count -eq 0) { 
+    LogError "Could not locate npx. Install NodeJS (includes npm and npx) https://nodejs.org/en/download/"
+    exit 1
+}
+
+if (!(Test-Path $CspellConfigPath)) {
+    LogError "Could not locate config file $CspellConfigPath"
+    exit 1
+}
+
+# Lists names of files that were in some way changed between the 
+# current ref and $TargetBranch. Excludes files that were deleted to
+# prevent errors in Resolve-Path
+Write-Host "git diff --diff-filter=d --name-only $TargetBranch $SourceBranch"
+$changedFiles = git diff --diff-filter=d --name-only $TargetBranch $SourceBranch `
+    | Resolve-Path
+
+$changedFilesCount = ($changedFiles | Measure-Object).Count
+Write-Host "Git Detected $changedFilesCount changed file(s). Files checked by cspell may exclude files according to cspell.json"
+
+if ($changedFilesCount -eq 0) {
+    Write-Host "No changes detected"
+    exit 0
+}
+
+$changedFilesString = $changedFiles -join ' '
+
+Write-Host "npx cspell --config $CspellConfigPath $changedFilesString"
+$spellingErrors = Invoke-Expression "npx cspell --config $CspellConfigPath $changedFilesString"
+
+if ($spellingErrors) {
+    foreach ($spellingError in $spellingErrors) { 
+        LogWarning $spellingError
+    }
+    LogWarning "Spelling errors detected. To correct false positives or learn about spell checking see: https://aka.ms/azsdk/engsys/spellcheck"
+}
+
+exit 0
+
+<#
+.SYNOPSIS
+Uses cspell (from NPM) to check spelling of recently changed files
+
+.DESCRIPTION
+This script checks files that have changed relative to a base branch (default 
+`master`) for spelling errors. Dictionaries and spelling configurations reside 
+in a configurable `cspell.json` location.
+
+This script uses `npx` and assumes that NodeJS (and by extension `npm` and `npx`
+) are installed on the machine. If it does not detect `npx` it will warn the 
+user and exit with an error. 
+
+The entire file is scanned, not just changed sections. Spelling errors in parts 
+of the file not touched will still be shown.
+
+Running this on the local machine will trigger tests 
+
+.PARAMETER TargetBranch
+Git ref to compare changes. This is usually the "base" (GitHub) or "target" 
+(DevOps) branch for which a pull request would be opened.
+
+.PARAMETER SouceBranch
+Git ref to use instead of changes in current repo state. Use `HEAD` here to 
+check spelling of files that have been committed and exlcude any new files or
+modified files that are not committed. This is most useful in CI scenarios where
+builds may have modified the state of the repo.
+
+.PARAMETER CspellConfigPath
+Optional location to use for cspell.json path. Default value is 
+`./.vscode/cspell.json`
+
+.EXAMPLE
+./eng/common/scripts/Test-Spelling.ps1 -TargetBranch 'target_branch_name'
+
+This will run spell check with changes in the current branch with respect to 
+`target_branch_name`
+
+#>