Use field to replace a few more explicit ThreadStatic fields

[stephentoub]

No description provided.

[Copilot]

Pull Request Overview

This PR modernizes ThreadStatic field patterns by replacing explicit ThreadStatic field declarations with the newer field keyword syntax in auto-properties. This simplifies the code by eliminating the need for separate backing fields and getter/setter logic.

Key changes:

• Replaces [ThreadStatic] private static Type? t_field; patterns with [field: ThreadStatic] on auto-properties
• Consolidates multi-line property implementations into single-line expressions using field ??= new()
• Removes redundant backing fields and associated boilerplate code

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
System/Transactions/Transaction.cs	Converts ContextData ThreadStatic field to use field keyword in TLSCurrentData property
CoseTestHelpers.cs	Simplifies TestKeyRing ThreadStatic property using field keyword
System/Diagnostics/Debug.cs	Updates IndentLevel ThreadStatic property to use field keyword
RandomNumberGenerator.cs	Converts Current property ThreadStatic backing field to field keyword
ImportType.cs	Simplifies CastSingleValueCache ThreadStatic property using field keyword
ContractNameServices.cs	Updates TypeIdentityCache ThreadStatic property to use field keyword
LazyAsyncResult.cs	Converts CurrentThreadContext ThreadStatic property to use field keyword