Add aria label hint for keyboard deletion of chat attachments

[Copilot]

Screen reader users had no way to discover that Delete/Backspace removes attached context files in Chat.

Adds a (Delete) suffix to attachment aria labels when deletion is supported. The hint is gated on the same conditions as the existing keyboard handler (supportsDeletion && !attachment.range).

• Added _hasClearButton flag and appendDeletionHint() helper in AbstractChatAttachmentWidget
• Updated all 13 attachment widget subclasses to pipe their aria labels through appendDeletionHint()
• Added missing aria label and deletion hint to PromptTextAttachmentWidget
• Fixed ImageAttachmentWidget and NotebookCellOutputChatAttachmentWidget.renderImageOutput to pass local ariaLabel variable directly to appendDeletionHint() instead of reading back from this.element.ariaLabel

Before: "Attached file, main.ts /src"
After: "Attached file, main.ts /src (Delete)"

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[meganrogge]

@copilot, it should just say (Delete) in parens, not that long message

[Copilot]

@copilot, it should just say (Delete) in parens, not that long message

Updated in f55762a. The hint is now (Delete) — e.g. "Attached file, main.ts /src (Delete)".

[Copilot]

Pull request overview

This PR improves accessibility for screen reader users in VS Code's Chat panel by adding a deletion hint to the aria labels of chat attachment widgets. When an attachment supports keyboard deletion (Delete/Backspace), its aria label now includes ", press Delete to remove from context" so screen reader users can discover this capability.

Changes:

• Added _hasClearButton flag and appendDeletionHint() helper method to AbstractChatAttachmentWidget base class, which appends a localized deletion hint only when the clear button is active.
• Set _hasClearButton = true inside attachClearButton() to track whether deletion is supported.
• Updated 12 of the 13 attachment widget subclasses to pipe their aria labels through appendDeletionHint().

Comments suppressed due to low confidence (2)

src/vs/workbench/contrib/chat/browser/attachments/chatAttachmentWidgets.ts:445

• In ImageAttachmentWidget, appendDeletionHint is called with this.element.ariaLabel ?? '' even though the local ariaLabel variable (defined earlier in the constructor) is still in scope and would be more direct and robust. Reading from this.element.ariaLabel is fragile because it depends on createImageElements having set it; a future refactor of that function could silently break the hint.

		this.element.ariaLabel = this.appendDeletionHint(this.element.ariaLabel ?? '');

src/vs/workbench/contrib/chat/browser/attachments/chatAttachmentWidgets.ts:936

• In NotebookCellOutputChatAttachmentWidget.renderImageOutput, appendDeletionHint is called with this.element.ariaLabel ?? '' even though the local ariaLabel variable is still in scope. Using the local variable directly is more robust: it doesn't depend on createImageElements having set element.ariaLabel.

		this.element.ariaLabel = this.appendDeletionHint(this.element.ariaLabel ?? '');