Remove lost links (and a few manual anchors)

[gewarren]

Contributes to #10722.

(Hide whitespace changes.)

[Copilot]

Pull request overview

This PR cleans up .NET API reference XML docs by removing manual HTML anchors and eliminating or fixing malformed / “lost” links, relying more on DocFX’s generated heading anchors and stable Learn URLs.

Changes:

• Removed manual <a name="..."> anchors and updated intra-page links to match generated heading IDs.
• Removed or corrected malformed external links (notably several learn.microsoft.com URLs).
• Normalized some markdown formatting (lists, spacing, and minor punctuation tweaks).

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
xml/System/String.xml	Removes a manual anchor before a formatting example section.
xml/System/Math.xml	Removes manual anchors and updates intra-page links / remarks formatting around Math.Round.
xml/System/DateTime.xml	Updates section links to generated heading IDs; removes manual anchors.
xml/System.Xml.Serialization.Advanced/SchemaImporterExtension.xml	Removes malformed CodeDOM reference links; adjusts repeated remarks text.
xml/System.Windows/AttachedPropertyBrowsableForChildrenAttribute.xml	Minor spacing cleanup in remarks text.
xml/System.Windows.Media.Effects/ShaderEffect.xml	Reflows remarks content and removes a malformed external reference.
xml/System.Windows.Controls/TabItem.xml	Removes a lost link in “Customizing” section.
xml/System.Windows.Controls/TabControl.xml	Removes a lost link in “Customizing” section.
xml/System.Threading/Lock.xml	Fixes Learn URL format for the C# lock-object proposal link.
xml/System.Text/Encoding.xml	Updates a Learn blog URL to non-localized form.
xml/System.Runtime.InteropServices/PrimaryInteropAssemblyAttribute.xml	Removes malformed external links in remarks.
xml/System.Runtime.InteropServices/InterfaceTypeAttribute.xml	Cleans up malformed external references and markdown formatting.
xml/System.Runtime.InteropServices/DispIdAttribute.xml	Removes malformed external link and normalizes markdown formatting.
xml/System.Runtime.InteropServices/CoClassAttribute.xml	Removes malformed external reference and normalizes markdown formatting.
xml/System.Net/WebRequest.xml	Removes malformed external links and leaves type names as plain text in remarks.
xml/System.Management.Instrumentation/WmiProviderInstallationException.xml	Removes malformed MI APIs link and simplifies guidance text.
xml/System.Diagnostics/Process.xml	Normalizes markdown list formatting and spacing in remarks/notes; minor text cleanup.