fix: make hosted plugin support testable

Hide the concrete implementation behind an interface so that tests can
`require` it.

Signed-off-by: Akos Kitta <a.kitta@arduino.cc>

arduino-ide-extension/src/browser/hosted/hosted-plugin-support.ts

@@ -0,0 +1,14 @@
+import type { Event } from '@theia/core/lib/common/event';
+
+/*
+This implementation hides the default HostedPluginSupport implementation from Theia to be able to test it.
+Otherwise, the default implementation fails at require time due to the `import.meta` in the Theia plugin worker code.
+https://github.com/eclipse-theia/theia/blob/964f69ca3b3a5fb87ffa0177fb300b74ba0ca39f/packages/plugin-ext/src/hosted/browser/plugin-worker.ts#L30-L32
+*/
+
+export const HostedPluginSupport = Symbol('HostedPluginSupport');
+export interface HostedPluginSupport {
+  readonly didStart: Promise<void>;
+  readonly onDidLoad: Event<void>;
+  readonly onDidCloseConnection: Event<void>;
+}