feat: add search functionality to Topics view

[shouples]

Summary of Changes

Closes #1002.

The Topics view is now searchable with the same general mechanisms as the Resources view search done in #996, specifically to allow searching by topic name and schema subject.

topics-view-search.mov

Any additional details or context that should be provided?

Highlighting this part specifically:

vscode/src/loaders/loaderUtils.ts

Lines 85 to 91 in 8789c31

	// HACK: we need to create children to allow searching the Topics view by schema subject; this
	// will only allow the topic to "match" and be returned from the TopicsViewProvider's
	// `getChildren()` method, and then once the topic is expanded, it will show the real subject
	// container(s), which will be the source of truth for subjects+schemas
	const subjectChildren: ContainerTreeItem<Schema>[] = matchingSubjects.map(
	(subject) => new ContainerTreeItem<Schema>(subject, TreeItemCollapsibleState.Collapsed, []),
	);

The search logic is fundamentally about what items are returned at each level of the tree data. The topics view is responsible for two main things upon loading at the root level: listing topics, and listing schema subjects to decorate the topics. Based on those two facts, the above snippet ensures we can search for a subject by preemptively setting a topic's children to be empty subject containers. If a Kafka topic matches based on its subject, it can then go through the normal motions of expanding to show the real subject container here:

vscode/src/viewProviders/topics.ts

Lines 131 to 134 in 8789c31

	// NOTE: we end up here when expanding a (collapsed) treeItem
	if (element instanceof KafkaTopic) {
	// return schema-subject containers
	children = await loadTopicSchemas(element);

...which we then are able to expand further and see all associated schema versions due to the subject container matching:

vscode/src/viewProviders/topics.ts

Lines 152 to 154 in 8789c31

	// if the parent item matches the search string, return all children so the user can expand
	// and see them all, even if just the parent item matched and shows the highlight(s)
	const parentMatched = element && itemMatchesSearch(element, this.itemSearchString);

All this to say: we can't search by any other pieces of information about a schema unless we eagerly load them and make sure they're available in the earlier-mentioned-empty-container-hack within loaderUtils.ts.

Pull request checklist

Please check if your PR fulfills the following (if applicable):

Tests

• Added new
• Updated existing
• Deleted existing

Other

• All new disposables (event listeners, views, channels, etc.) collected as for eventual cleanup?

• Does anything in this PR need to be mentioned in the user-facing CHANGELOG or README?
• Have you validated this change locally by packaging and installing the extension .vsix file?

  gulp clicktest

[shouples]

This mainly ensures we don't over-match while searching for a subject. It isn't currently possible to search for a schema ID in the Topics view since we don't have any eagerly-fetched Schemas to attach to the subject container tree items, just the subjects themselves.

[shouples]

Unrelated to this PR: later versions of @types/vscode provide id: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/ab4715a8aead1731ced56619128c31e57bcc682d/types/vscode/index.d.ts#L904-L909

[shouples]

This is done internally by VS Code as well, just not available to extensions
https://github.com/DefinitelyTyped/DefinitelyTyped/blob/ab4715a8aead1731ced56619128c31e57bcc682d/types/vscode/index.d.ts#L11903-L11908

[shouples]

Unrelated to this PR: another EnvironmentId branded type fix