JDT.LS binary download does not honour VS Code http.proxy setting in corporate networks

从 src/extension.ts 和下载工具开始，然后确定哪个 HTTP 客户端负责处理 JDT.LS 下载，以及其 agent 配置是如何传递的。检查 issue 中描述的 VS Code http 设置以及 HTTPS_PROXY/HTTP_PROXY 输入。完成的标准是：下载（包括更新）能够通过经过身份验证的代理工作，且不会出现报告的静默超时。

Problem

On first install (or when the extension downloads a JDT.LS update), the download fails silently in corporate environments that require an authenticated HTTPS proxy. VS Code exposes the proxy via http.proxy and http.proxyAuthorization settings, and also via HTTPS_PROXY / HTTP_PROXY environment variables injected into the extension host. However, the extension's download logic (in src/extension.ts and the download utility) does not read these and passes no proxy configuration to its HTTP client.

Steps to Reproduce

1. In a corporate environment, set:

   "http.proxy": "http://proxy.corp.example.com:8080",
   "http.proxyStrictSSL": false
   

2. Install the extension on a machine that has no prior JDT.LS installation.
3. Open a Java file. The status bar shows "Downloading Java support..." indefinitely.
4. No error appears; the Output → Java channel shows a TCP timeout to download.jboss.org or the GitHub releases CDN.

Expected Behaviour

The extension should detect the proxy from vscode.workspace.getConfiguration('http').get('proxy') or process.env.HTTPS_PROXY and configure its HTTP download agent accordingly (e.g., via https-proxy-agent or equivalent).

Workaround (not acceptable)

Users currently have to pre-download JDT.LS manually, which is not discoverable and breaks on updates.

Proposed Fix

import HttpsProxyAgent from 'https-proxy-agent';
const proxyUrl = vscode.workspace.getConfiguration('http').get<string>('proxy')
  ?? process.env.HTTPS_PROXY ?? process.env.HTTP_PROXY;
const agent = proxyUrl ? new HttpsProxyAgent(proxyUrl) : undefined;
// Pass agent to node-fetch / got / axios download client

Environment

• OS: Windows 11 Enterprise 10.0.26200 (mandatory corporate proxy, no direct internet)
• VS Code: 1.89+
• Extension: redhat.java latest