Refactor LanguageClientConsumer to wait properly

This makes a lot more sense and fixes a long-standing bug.  Also cleaned up a
lot while at it.

1. `SessionManager` is created and the features are injected into the session
manager with the intention of them being able to "register" their language
client event handlers in the period between when the client is created and when
it is started.

2. For each feature, if it gets to a point where it needs the language client,
we want them to wait on a promise for the "started" client to be provided from
the session manager before continuing.

3. Once it is started, the session manager passes the client to
`LanguageClientConsumer` which resolves the promise for the features so they can
continue.

Author: andyleejordan

src/features/CodeActions.ts

@@ -5,25 +5,25 @@ import vscode = require("vscode");
 import { ILogger } from "../logging";
 
 export class CodeActionsFeature implements vscode.Disposable {
-    private showDocumentationCommand: vscode.Disposable;
+    private command: vscode.Disposable;
 
     constructor(private log: ILogger) {
         // NOTE: While not exposed to the user via package.json, this is
         // required as the server's code action sends across a command name.
         //
         // TODO: In the far future with LSP 3.19 the server can just set a URL
         // and this can go away. See https://github.com/microsoft/language-server-protocol/issues/1548
-        this.showDocumentationCommand =
+        this.command =
             vscode.commands.registerCommand("PowerShell.ShowCodeActionDocumentation", async (ruleName: string) => {
                 await this.showRuleDocumentation(ruleName);
             });
     }
 
     public dispose(): void {
-        this.showDocumentationCommand.dispose();
+        this.command.dispose();
     }
 
-    public async showRuleDocumentation(ruleId: string): Promise<void> {
+    private async showRuleDocumentation(ruleId: string): Promise<void> {
         const pssaDocBaseURL = "https://docs.microsoft.com/powershell/utility-modules/psscriptanalyzer/rules/";
 
         if (!ruleId) {

src/features/Console.ts

@@ -200,8 +200,8 @@ export class ConsoleFeature extends LanguageClientConsumer {
                 } else {
                     selectionRange = editor.document.lineAt(editor.selection.start.line).range;
                 }
-
-                await this.languageClient?.sendRequest(EvaluateRequestType, {
+                const client = await LanguageClientConsumer.getLanguageClient();
+                await client.sendRequest(EvaluateRequestType, {
                     expression: editor.document.getText(selectionRange),
                 });
 
@@ -217,19 +217,19 @@ export class ConsoleFeature extends LanguageClientConsumer {
         for (const command of this.commands) {
             command.dispose();
         }
+
         for (const handler of this.handlers) {
             handler.dispose();
         }
     }
 
-    public override setLanguageClient(languageClient: LanguageClient): void {
-        this.languageClient = languageClient;
+    public override onLanguageClientSet(languageClient: LanguageClient): void {
         this.handlers = [
-            this.languageClient.onRequest(
+            languageClient.onRequest(
                 ShowChoicePromptRequestType,
                 (promptDetails) => showChoicePrompt(promptDetails)),
 
-            this.languageClient.onRequest(
+            languageClient.onRequest(
                 ShowInputPromptRequestType,
                 (promptDetails) => showInputPrompt(promptDetails)),
         ];