Sync eng/common directory with azure-sdk-tools for PR 11330 (#6683)

* Add shell script for spell check

* Add shebang and make cspell script executable for bash invocation

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Apply suggestion from @benbp

---------

Co-authored-by: Fan Yang <yangfan@microsoft.com>
Co-authored-by: Ben Broderick Phillips <bebroder@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

eng/common/spelling/Invoke-Cspell.ps1

@@ -1,3 +1,5 @@
+#!/usr/bin/env pwsh
+
 <#
 .SYNOPSIS
 Invokes cspell using dependencies defined in adjacent ./package*.json

eng/common/spelling/README.md

@@ -0,0 +1,84 @@
+# Spelling Check Scripts
+
+This directory contains a script to run cspell (Code Spell Checker) on the repository using the dependencies defined in the adjacent `package*.json` files.
+
+## Adding Legitimate Words
+
+If the spell checker flags legitimate words as misspelled, you can add them to the dictionary configuration file located at `.vscode/cspell.json`.
+
+### Where to Add Words
+
+There are two main places to add legitimate words. Maintain alphabetical order when adding words to keep the dictionary organized:
+
+1. **Root-level words array**: Add words to the `"words"` array at the root level of the configuration file. This is the preferred location for project-specific terms, technical vocabulary, and commonly used words.
+
+2. **Baseline dictionary**: Add words to the `"baseline"` dictionary under `"dictionaryDefinitions"`. This is typically used for words that were already present in the codebase when the spell checker was first introduced.
+
+
+### Example
+
+To add new words, edit `.vscode/cspell.json` and add them to the `"words"` array:
+
+```json
+{
+    "words": [
+        "myprojectname",
+        "customterm",
+        "technicalword"
+    ]
+}
+```
+
+### Guidelines
+
+- Use lowercase for words
+- Consider whether the word is truly legitimate or if it might be a typo
+
+## Available Scripts
+
+### PowerShell Version (Windows)
+- **File**: `Invoke-Cspell.ps1`
+- **Usage**: For Windows PowerShell environments
+
+## Usage Examples
+
+```powershell
+# Check all files (default)
+./eng/common/spelling/Invoke-Cspell.ps1
+
+# Check specific files
+./eng/common/spelling/Invoke-Cspell.ps1 -ScanGlobs 'sdk/*/*/PublicAPI/**/*.md'
+
+# Check multiple globs (powershell invocation only)
+./eng/common/spelling/Invoke-Cspell.ps1 -ScanGlobs @('sdk/storage/**', 'sdk/keyvault/**')
+
+# Check single file
+./eng/common/spelling/Invoke-Cspell.ps1 -ScanGlobs './README.md'
+```
+
+## Parameters
+
+- **Job Type**: The cspell command to run (default: `lint`)
+- **Scan Globs**: File patterns to check for spelling
+- **Config Path**: Location of the cspell.json configuration file
+- **Spell Check Root**: Root directory for relative paths
+- **Package Cache**: Working directory for npm dependencies
+- **Leave Cache**: Option to preserve the npm package cache
+
+## Requirements
+
+- Node.js and npm must be installed
+- The `.vscode/cspell.json` configuration file must exist
+- `jq` command-line JSON processor (for bash version)
+
+## How It Works
+
+1. Creates a temporary working directory for npm packages
+2. Copies `package.json` and `package-lock.json` to the working directory
+3. Installs npm dependencies using `npm ci`
+4. Modifies the cspell configuration to include specified file globs
+5. Runs cspell with the modified configuration
+6. Restores the original configuration
+7. Cleans up temporary files
+
+The scripts ensure that a LICENSE file (or temporary file) is always included in the scan to meet cspell's requirements for the "files" array.