Ensure dashboard tabs only show for supported providers (#1798)

- Fixes #1764, fixes #1765
- Fixes bug where configModifiers were passed in the dashboard service in some places, and a different object with incompatible / missing fields in a different one. Now it always passes in the owner object, and this should have the required fields
 - Note: this doesn't fix the problem where the code does not fail to build, which I would have expected to be the case.
- Adds "provider" as an option for TabConfig including in the schema
- Filter by "provider" type when loading tabs. If provider is not set for a tab, will assume "MSSQL" since it's the default provider. This is a design decision - without this, we would either have to disable tabs that don't show this or have them incorrectly show for non-MSSQL provider types

Notes:

Does not override behavior for individual widgets, which still get the current provider set as their provider if not specified. This seems to be required so should be fine.
We will fix tasks/widgets that aren't supported by a provider showing up in a separate PR, since it's a different issue

src/sql/platform/dashboard/common/dashboardRegistry.ts

@@ -7,7 +7,6 @@ import { Registry } from 'vs/platform/registry/common/platform';
 import { IConfigurationRegistry, Extensions as ConfigurationExtension } from 'vs/platform/configuration/common/configurationRegistry';
 import { IJSONSchema, IJSONSchemaMap } from 'vs/base/common/jsonSchema';
 import * as nls from 'vs/nls';
-import { deepClone } from 'vs/base/common/objects';
 import { IExtensionPointUser, ExtensionsRegistry } from 'vs/workbench/services/extensions/common/extensionsRegistry';
 
 import { ProviderProperties } from 'sql/parts/dashboard/widgets/properties/propertiesWidget.component';
@@ -22,6 +21,7 @@ export const Extensions = {
 export interface IDashboardTab {
 	id: string;
 	title: string;
+	provider: string | string[];
 	publisher: string;
 	description?: string;
 	container?: object;