Add Uri.UriSchemeData constant

[Copilot]

Description

Adds UriSchemeData constant to System.Uri for data: URIs, following the pattern established in .NET 6 for adding scheme constants.

namespace System
{
    public partial class Uri
    {
        /// <summary>Specifies that the URI is a data URI.</summary>
        public static readonly string UriSchemeData = "data";
    }
}

Changes:

• Added UriSchemeData field to System.Private.Uri/src/System/Uri.cs with XML documentation comment
• Added corresponding declaration to System.Runtime/ref/System.Runtime.cs

Customer Impact

Enables use of Uri.UriSchemeData instead of hardcoding "data" when working with data URIs.

Regression

No, this is a new API addition.

Testing

All existing Uri tests pass. Build succeeds with 0 warnings and 0 errors.

Risk

Minimal. Additive API only—no behavioral changes to existing code.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Consider adding Uri.UriSchemeData</issue_title>
<issue_description>### Is your feature request related to a problem? Please describe.

We have constants for http, https, etc., but not for data: URIs.

Describe the solution you'd like

A new constant in the System.Uri class:

namespace System
{
    public partial class Uri
    {
        public static readonly string UriSchemeHttp;
        public static readonly string UriSchemeHttps;
        // +14 other schemes following the same pattern

+       public static readonly string UriSchemeData = "data";
    }
}

Additional context

n/a</issue_description>

Comments on the Issue (you are @copilot in this section)

@MihaZupan Sounds like a reasonable thing to add, we opened the door to adding more constants here with .NET 6 https://github.com//issues/35180#issuecomment-670645017. `data` feels common enough to include.

For reference here's the current list

runtime/src/libraries/System.Private.Uri/src/System/Uri.cs

Lines 22 to 37 in ffb52e9

	public static readonly string UriSchemeFile = UriParser.FileUri.SchemeName;
	public static readonly string UriSchemeFtp = UriParser.FtpUri.SchemeName;
	public static readonly string UriSchemeSftp = "sftp";
	public static readonly string UriSchemeFtps = "ftps";
	public static readonly string UriSchemeGopher = UriParser.GopherUri.SchemeName;
	public static readonly string UriSchemeHttp = UriParser.HttpUri.SchemeName;
	public static readonly string UriSchemeHttps = UriParser.HttpsUri.SchemeName;
	public static readonly string UriSchemeWs = UriParser.WsUri.SchemeName;
	public static readonly string UriSchemeWss = UriParser.WssUri.SchemeName;
	public static readonly string UriSchemeMailto = UriParser.MailToUri.SchemeName;
	public static readonly string UriSchemeNews = UriParser.NewsUri.SchemeName;
	public static readonly string UriSchemeNntp = UriParser.NntpUri.SchemeName;
	public static readonly string UriSchemeSsh = "ssh";
	public static readonly string UriSchemeTelnet = UriParser.TelnetUri.SchemeName;
	public static readonly string UriSchemeNetTcp = UriParser.NetTcpUri.SchemeName;
	public static readonly string UriSchemeNetPipe = UriParser.NetPipeUri.SchemeName;

</comment_new>
<comment_new>@bartonjs

• Looks good as proposed

namespace System
{
    public partial class Uri
    {
        public static readonly string UriSchemeData = "data";
    }
}
```</body></comment_new>
</comments>

• Fixes Consider adding Uri.UriSchemeData #122020

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[Copilot]

Pull request overview

This PR adds a new constant UriSchemeData = "data" to the System.Uri class to enable developers to reference the data: scheme without hardcoding string literals, following the pattern established for other URI schemes.

Changes:

• Added UriSchemeData constant to the implementation in System.Private.Uri
• Added corresponding reference assembly declaration in System.Runtime

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Private.Uri/src/System/Uri.cs	Adds the UriSchemeData = "data" constant at the end of the URI scheme constants list
src/libraries/System.Runtime/ref/System.Runtime.cs	Adds the UriSchemeData declaration in alphabetical order in the reference assembly

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