Design reusable HTML error block for tooltips

[shouples]

Initial use-case for an error block is in the Resources view for any "direct" connections that return a FAILED connection status, starting with #944:

So far we've only used markdown in tooltip content, but VS Code also supports tooltips with HTML (when enabled by the extension). We may be able to add some better styling to the error block based on available tags and attributes.

Any adjustments to our existing tooltips will likely need to explicitly set supportHtml for the MarkdownString instance or override the default:

vscode/src/models/main.ts

Lines 42 to 61 in 1cd92f7

	/**
	* This is a custom tooltip class that extends `vscode.MarkdownString` to add constructor arguments
	* for additional properties that are not available in the base class.
	* @param value Optional, initial value.
	* @param isTrusted Whether the markdown content is trusted or not (e.g. to support embedding
	* command-markdown syntax). (Default is `true`.)
	* @param supportHtml Whether the tooltip supports HTML content. (Default is `false`.)
	* @param supportThemeIcons Whether the tooltip supports the extension's custom contributed icons in
	* the markdown string (e.g. `$(confluent-environment)`). (Default is `true`.)
	*/
	export class CustomMarkdownString extends vscode.MarkdownString {
	constructor(
	value?: string,
	public isTrusted: boolean = true,
	public supportHtml: boolean = false,
	public supportThemeIcons: boolean = true,
	) {
	super(value, supportThemeIcons);
	}
	}