feat: save initialize params

This is useful for accessing experimental client capabilities on the
server.

Author: chrismwendt

src/extension/api.ts

@@ -1,7 +1,7 @@
 import { Subscription } from 'rxjs'
 import { Context } from '../environment/context/context'
 import { MessageConnection } from '../jsonrpc2/connection'
-import { Settings } from '../protocol'
+import { InitializeParams, Settings } from '../protocol'
 import { URI } from '../types/textDocument'
 
 /**
@@ -10,6 +10,11 @@ import { URI } from '../types/textDocument'
  * @template C the extension's settings
  */
 export interface CXP<C = Settings> {
+    /**
+     * The params passed by the client in the `initialize` request.
+     */
+    initializeParams: InitializeParams
+
     /**
      * The root URI of the workspace in which this extension is running.
      *

src/extension/extension.ts

@@ -25,6 +25,7 @@ class ExtensionHandle<C> implements CXP<C> {
     constructor(public readonly rawConnection: MessageConnection, public readonly initializeParams: InitializeParams) {
         this.subscription.add(this.rawConnection)
 
+        this.initializeParams = initializeParams
         this.configuration = createExtConfiguration<C>(
             this,
             initializeParams.configurationCascade as ConfigurationCascade<C>