fix(settings): "accessing configuration without providing a resource"

Problem:
vscode extension host logs show many warnings like this:

    [warning] [amazonwebservices.aws-toolkit-vscode] Accessing a resource scoped configuration without providing a resource is not expected.
    To get the effective value for 'files.watcherExclude', provide the URI of a resource or 'null' for any resource

Solution:
Default to `null` instead of `undefined` when getting a config.

Author: justinmk3

src/shared/settings.ts

@@ -151,7 +151,8 @@ export class Settings {
      * The resulting configuration object should not be cached.
      */
     private getConfig(section?: string) {
-        return this.workspace.getConfiguration(section, this.scope)
+        // eslint-disable-next-line no-null/no-null
+        return this.workspace.getConfiguration(section, this.scope ?? null)
     }
 
     /**
@@ -167,7 +168,7 @@ export class Settings {
     static #instance: Settings
 
     /**
-     * A singleton scoped to the global configuration target.
+     * A singleton scoped to the global configuration target and `null` resource.
      */
     public static get instance() {
         return (this.#instance ??= new this())