src/vs/platform/userDataSync/common/ignoredExtensions.ts/IgnoredExtensionsManagementService/getIgnoredExtensions
class IgnoredExtensionsManagementService:	getIgnoredExtensions(installed: ILocalExtension[]): string[] {
		const defaultIgnoredExtensions = installed.filter(i => i.isMachineScoped).map(i => i.identifier.id.toLowerCase());
		const value = this.getConfiguredIgnoredExtensions().map(id => id.toLowerCase());
		const added: string[] = [], removed: string[] = [];
		if (Array.isArray(value)) {
			for (const key of value) {
				if (key.startsWith('-')) {
					removed.push(key.substring(1));
				} else {
					added.push(key);
				}
			}
		}
		return distinct([...defaultIgnoredExtensions, ...added,].filter(setting => removed.indexOf(setting) === -1));
	}