Fix URI edge case issue

[lilinus]

Fixes #110480

[Copilot]

Pull Request Overview

This PR fixes a URI edge case by adjusting the offset calculations during URI parsing and adding a test case to validate the behavior when leading whitespace and Unicode characters are present.

• Updated the offset assignments for scheme, user, and host in the URI parsing logic.
• Added a new functional test to verify URI construction under edge-case conditions in Windows and non-Windows environments.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/libraries/System.Private.Uri/tests/FunctionalTests/UriTests.cs	Added a new test verifying the behavior of URI parsing with leading whitespace and Unicode.
src/libraries/System.Private.Uri/src/System/Uri.cs	Updated offset fields in the URI parsing method to address the edge-case bug.

Comments suppressed due to low confidence (2)

src/libraries/System.Private.Uri/tests/FunctionalTests/UriTests.cs:805

• [nitpick] Consider adding an inline comment explaining the intention behind the chosen URI string format and handling of leading whitespace/unicode characters for clarity in future maintenance.

            string uriString = PlatformDetection.IsWindows ? "\tC:\\\u005C" : "\t/\u005C";

src/libraries/System.Private.Uri/src/System/Uri.cs:3301

• [nitpick] It might be beneficial to document why the offset fields for User and Host are set to the current string length immediately after setting the Scheme offset, to aid future maintainers in understanding the edge-case handling.

                    _info.Offset.Scheme = 0;

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[MihaZupan]

Test failures are related

[MihaZupan]

Thank you