Fix Invoke-RestMethod to support read-only files in multipart form data

[yotsuda]

Summary

This PR fixes issue #25482 where Invoke-RestMethod and Invoke-WebRequest fail when uploading read-only files via the -Form parameter.

Changes

Code Fix

• File: src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/Common/WebRequestPSCmdlet.Common.cs
• Change: Added FileAccess.Read parameter to FileStream constructor in GetMultipartFileContent() method
• Impact: Allows read-only files to be uploaded successfully

Test Coverage

• File: test/powershell/Modules/Microsoft.PowerShell.Utility/WebCmdlets.Tests.ps1
• Added Tests:
  • Invoke-WebRequest -Form supports read-only file values
  • Invoke-RestMethod -Form supports read-only file values
• Test Coverage: Both cmdlets are tested with read-only files, including proper cleanup

Root Cause

The GetMultipartFileContent() method was opening files with FileMode.Open without specifying FileAccess, which defaults to FileAccess.ReadWrite. This caused an "Access denied" error when attempting to upload read-only files.

Fix

Changed the FileStream initialization from:

new FileStream(file.FullName, FileMode.Open)

To:

new FileStream(file.FullName, FileMode.Open, FileAccess.Read)

Since the file is only being read for upload, FileAccess.Read is the correct access mode and allows read-only files to be processed.

Related Issue

Fixes #25482

[iSazonov]

I wonder what is changed here?

[yotsuda]

I apologize for the inconvenience. A UTF-8 BOM was accidentally added to the file during editing. I've fixed this in commit 8fe4fed.