feat: implement rate limit warning banner and associated parameters

[ethanyhou]

Test:

1. With handoff:

2. Without handoff:

3. The banner should be hide/unhide when check chat history.

[Copilot]

Pull request overview

Adds end-to-end support for showing a rate-limit warning banner in the Eclipse Chat UI when the language server emits a new $/copilot/rateLimitWarning notification.

Changes:

• Introduces a reusable StaticBanner SWT widget (message + inline link + dismiss).
• Adds a new LSP notification params record (RateLimitWarningParams) and client handler to forward it via the event broker.
• Wires Chat UI to listen for the new event topic and render/dispose the banner, plus new i18n strings and a docs URL constant.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/i18n/messages.properties	Adds new localized strings for the banner text/link/dismiss tooltip.
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/i18n/Messages.java	Exposes the new i18n keys as Messages.* fields.
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/chat/StaticBanner.java	New reusable banner widget implementation.
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/chat/ChatView.java	Subscribes to the new rate-limit warning topic and instructs the ActionBar to show the banner.
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/chat/ActionBar.java	Adds creation/disposal methods for the banner and clears it on new conversation.
com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/UiConstants.java	Adds the “rate limit info” URL constant used by the banner.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/protocol/RateLimitWarningParams.java	New protocol record type for the notification payload.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/CopilotLanguageClient.java	Handles $/copilot/rateLimitWarning and forwards it onto the Eclipse event broker.
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/events/CopilotEventConstants.java	Adds a new event topic constant for rate-limit warnings.