Expose HttpError to plugins

This will let them throw and show nice errors more easily.

test/plugin.test.ts

@@ -2,6 +2,7 @@ import { logger } from "@coder/logger"
 import * as express from "express"
 import * as fs from "fs"
 import * as path from "path"
+import { HttpCode } from "../src/common/http"
 import { PluginAPI } from "../src/node/plugin"
 import * as apps from "../src/node/routes/apps"
 import * as httpserver from "./httpserver"
@@ -81,4 +82,9 @@ describe("plugin", () => {
     ws.terminate()
     expect(message).toBe("hello")
   })
+
+  it("/test-plugin/error", async () => {
+    const resp = await s.fetch("/test-plugin/error")
+    expect(resp.status).toBe(HttpCode.LargePayload)
+  })
 })

test/test-plugin/src/index.ts

@@ -19,6 +19,9 @@ export const plugin: cs.Plugin = {
     r.get("/goland/icon.svg", (_, res) => {
       res.sendFile(fspath.resolve(__dirname, "../public/icon.svg"))
     })
+    r.get("/error", () => {
+      throw new cs.HttpError("error", cs.HttpCode.LargePayload)
+    })
     return r
   },