(#3600) Handle non-ASCII passwords with legacy encoding fallback

[AdmiringWorm]

Description Of Changes

Add a method to convert passwords to NetworkCredential using codepage 1252 encoding to support non-ASCII characters in credentials. This addresses issues with encoding mismatches in .NET 4.8.1 that cause incorrect password handling.

Update credential retrieval to use this conversion method, falling back to the original password on retry attempts to maintain compatibility.

Add tests verifying correct username and legacy-encoded password handling for non-ASCII characters in explicit and implicit credential scenarios.

Motivation and Context

Even when a user is using a password with non-ascii characters, we would still want the user to be able to connect to a remote source, even when

Testing

1. Update the credentials used for one of your sources to include non-ascii characters (ie, øæåéèàù)
2. Attempt to search for a package using the updated source with the new credentials.
3. Verify the expected results are shown.

Operating Systems Testing

• Windows 11

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v3 compatibility checked?

Related Issue

Fixes #3600