sts-vscode: fix extension api implementation

[Eskibear]

A patch for PR #751, otherwise it won't work. Fixing two problems:

• inconsistent name of argument between API definition and implmentation.
• didn't return the result in getLiveProcessData

[Eskibear]

BTW, you can test the APIs within a simple vscode extension, using below code snippet.

    const stsExt = vscode.extensions.getExtension("pivotal.vscode-spring-boot");
    const stsApi: ExtensionAPI = await stsExt?.activate();

    stsApi.onDidLiveProcessConnect(e => console.log("connect", e));
    stsApi.onDidLiveProcessDisconnect(e => console.log("disconnect", e));
    stsApi.onDidLiveProcessUpdate(async e => {
        console.log("update", e);
        const beans = await stsApi.getLiveProcessData({
            processKey: e,
            endpoint: "beans"
        });
        console.log(beans);
    });