Pub package name cache is not persisted

[DanTup]

The caching of the Pub package name cache is not working because of this code here:

Dart-Code/src/shared/vscode/workspace.ts

Lines 11 to 17 in 57a5511

	get extensionStoragePath(): string | undefined {
	const uri = this.context.globalStorageUri;
	const path = uri.scheme === "file" ? fsPath(uri) : undefined;
	if (path)
	mkDirRecursive(path);
	return path;
	}

The URI is now a vscode-userdata:/ URI and we only handle file.

We should isntead keep the URI and use workspace.fs to read/write this file.