Validate that an IPv6 Uri host is followed by expected delimiters

[MihaZupan]

For an input like http://[::]extra, we would previously hallucinate a slash after the ], so parsing would succeed and AbsolutePath would return /extra.

This change enforces that the ] is followed by a delimiter, same as we do for all other host types.

[Copilot]

Pull Request Overview

This PR fixes a URI parsing bug where IPv6 addresses followed by invalid characters (without proper delimiters) would incorrectly succeed and hallucinate path components. For example, http://[::]extra would previously parse successfully with /extra as the path, when it should fail.

Key Changes:

• Added validation to ensure IPv6 host addresses are followed by valid delimiters (:, /, ?, #, or end of string)
• Enhanced test coverage with multiple scenarios testing both invalid cases and valid delimiter combinations

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/src/System/Uri.cs	Added delimiter validation after IPv6 address parsing to reject malformed URIs
src/libraries/System.Private.Uri/tests/FunctionalTests/UriIpHostTest.cs	Refactored test helper and added comprehensive test cases for delimiter validation

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[rzikm]

LGTM