Backport System.Diagnostics.Process timing XML docs from runtime PR 130794

[Copilot]

This PR backports the Process timing-property documentation updates from dotnet/runtime#130794 into dotnet-api-docs. It aligns API reference behavior notes for post-exit access across Windows and Unix.

• StartTime

  • Replaced placeholder remarks with platform-specific behavior:
    • Windows: readable after exit if a process handle is available.
    • Unix: value is cached on first access; uncached post-exit access can fail.
  • Updated InvalidOperationException text to describe uncached/unavailable Unix and no-handle Windows cases.

• ExitTime

  • Added explicit InvalidOperationException documentation for access before process exit, missing association, and Windows no-handle scenarios.

• Processor timing properties (PrivilegedProcessorTime, TotalProcessorTime, UserProcessorTime)

  • Added platform behavior remarks for post-exit access (Windows available with handle, Unix unavailable).
  • Added InvalidOperationException and Win32Exception entries consistent with runtime behavior.
  • Updated summaries to match runtime wording intent for kernel/user/total CPU time semantics.

• Doc consistency and cleanup

  • Removed placeholder text and normalized remarks formatting in affected member docs.
  • Kept changes scoped to /xml/System.Diagnostics/Process.xml.

<exception cref="T:System.InvalidOperationException">
No process is associated with this object; on Windows, there is no process handle available; or on Unix, the value was not cached and is unavailable after the process exited.
</exception>

[Copilot]

Pull request overview

This PR backports documentation updates for System.Diagnostics.Process timing-related members to better describe platform-specific behavior (Windows vs Unix), especially for post-exit property access and associated exceptions.

Changes:

• Updated StartTime remarks and exceptions to describe Windows handle-based access and Unix caching/unavailability behavior.
• Added/updated exception documentation and platform behavior remarks for ExitTime and processor timing properties (PrivilegedProcessorTime, TotalProcessorTime, UserProcessorTime).
• Cleaned up placeholder content in affected member docs.

[adamsitnik]

@copilot address the feedback

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 4 comments.

[adamsitnik]

@gewarren please excuse me for bothering you again, but the new rules require a new approval after applying your suggesitons