Fix event handler documentation terminology to distinguish between event publishing and subscription

[Copilot]

The Visual Basic documentation for "How to call an event handler" was confusing because it didn't clearly distinguish between the two sides of events:

1. Event publishing - declaring events and raising them with RaiseEvent (which actually calls/invokes the event handlers)
2. Event subscription - subscribing to events with Handles/WithEvents or AddHandler (which sets up handlers to be called later)

Changes Made

Updated main article (how-to-call-an-event-handler.md):

• Changed title from "How to call an event handler" → "How to subscribe to events and handle them"
• Updated subheadings from "Call an event handler using..." → "Subscribe to an event using..."
• Added clear explanation distinguishing event publishing vs. subscription
• Clarified that RaiseEvent is what actually "calls" the event handlers
• Preserved all existing code examples (they demonstrate both concepts well)

Updated cross-references in 4 additional files to reflect the new title:

• Error documentation (bc33003.md)
• Related procedure documentation
• Table of contents

Problem Addressed

The original terminology was misleading:

• Title suggested you directly invoke event handlers
• Subheadings mentioned "calling" event handlers when describing subscription mechanisms
• Missing distinction between RaiseEvent (calls handlers) vs AddHandler/Handles (subscribe to events)

The documentation now clearly explains that subscribing to events is different from raising them, resolving the conceptual confusion identified in the issue.

Fixes #28033.

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Internal previews

📄 File	🔗 Preview link
docs/visual-basic/misc/bc33003.md	'Handles' is not valid on operator declaration
docs/visual-basic/programming-guide/language-features/procedures/how-to-call-a-procedure-that-does-not-return-a-value.md	How to: Call a Procedure that Does Not Return a Value (Visual Basic)
docs/visual-basic/programming-guide/language-features/procedures/how-to-call-an-event-handler.md	How to subscribe to events and handle them
docs/visual-basic/programming-guide/language-features/procedures/sub-procedures.md	Sub procedures (Visual Basic)
docs/visual-basic/programming-guide/language-features/procedures/toc.yml	docs/visual-basic/programming-guide/language-features/procedures/toc

[BillWagner]

This is ready for final review after accepting suggestions.