WorkspaceConfiguration update and inspect methods fail if section is undefined

[t1m0thyj]

Bug Description:

When vscode.workspace.getConfiguration() is called without providing a section identifier, then the update and inspect methods add an extra "undefined." in front of the dotted property name.

Expected behavior: config.update("x.y.z", true) should add the line "x.y.z": true to settings.json
Actual behavior: config.update("x.y.z", true) adds the line "undefined.x.y.z": true

Steps to Reproduce:

1. Create a VS Code extension that inspects/updates configuration values and install it into Theia. For example, add this code snippet:

   let config = vscode.workspace.getConfiguration();
   console.log(config.inspect("editor.tabSize"));
   await config.update("editor.tabSize", 8, vscode.ConfigurationTarget.Global);
   config = vscode.workspace.getConfiguration("editor");
   console.log(config.inspect("tabSize"));
   await config.update("tabSize", 8, vscode.ConfigurationTarget.Global);

2. Note that the first object logged to the console is wrong - the "defaultValue" should be 4 like the second object:

   2023-01-05T19:09:37.873Z root INFO [hosted-plugin: 44] {
     key: 'editor.tabSize',
     defaultValue: undefined,
     globalValue: undefined,
     workspaceValue: undefined,
     workspaceFolderValue: undefined
   }
   2023-01-05T19:09:38.059Z root INFO [hosted-plugin: 44] {
     key: 'tabSize',
     defaultValue: 4,
     globalValue: undefined,
     workspaceValue: undefined,
     workspaceFolderValue: undefined
   }
   

3. Also note that the contents of settings.json are wrong - the first property that starts with "undefined." is invalid:

   {
       "undefined.editor.tabSize": 8,
       "editor.tabSize": 8
   }

Additional Information

• Operating System: Alpine Linux (Docker)
• Theia Version: 1.33.0

I believe this is a regression that was introduced in #11393, and Theia 1.29.0 was the first version with this issue. In the following places, rawSection should not be hardcoded in case it is undefined:

theia/packages/plugin-ext/src/plugin/preference-registry.ts

Lines 171 to 173 in a733057

	update: (key: string, value: any, targetScope?: ConfigurationTarget | boolean, withLanguageOverride?: boolean): PromiseLike<void> => {
	const resourceStr = overrides.resource?.toString();
	const fullPath = `${overrides.overrideIdentifier ? `[${overrides.overrideIdentifier}].` : ''}${rawSection}.${key}`;

theia/packages/plugin-ext/src/plugin/preference-registry.ts

Lines 180 to 181 in a733057

	inspect: <T>(key: string): ConfigurationInspect<T> | undefined => {
	const path = `${rawSection}.${key}`;