Add --disable-file-cache flag (#8085)

The browser writes some workspace files to the client disk during normal
use. The webview service worker stores resources that have an ETag in
Cache Storage, and responses from /vscode-remote-resource can end up in
the HTTP disk cache. --disable-file-downloads does not cover either.

With --disable-file-cache, the webview resource loader sends no ETag for
a resource outside the webview's own extension, so the service worker
does not store it. /vscode-remote-resource responds with
`Cache-Control: no-store` for files outside the extension directories.
Extension files keep their ETags, so webviews still load extension code
from the cache. The flag is off by default.

src/node/cli.ts

@@ -51,6 +51,7 @@ export interface UserProvidedCodeArgs {
   "disable-update-check"?: boolean
   "disable-file-downloads"?: boolean
   "disable-file-uploads"?: boolean
+  "disable-file-cache"?: boolean
   "disable-workspace-trust"?: boolean
   "disable-getting-started-override"?: boolean
   "disable-proxy"?: boolean
@@ -193,6 +194,10 @@ export const options: Options<Required<UserProvidedArgs>> = {
     type: "boolean",
     description: "Disable file uploads.",
   },
+  "disable-file-cache": {
+    type: "boolean",
+    description: "Keep workspace files out of the browser cache.",
+  },
   "disable-workspace-trust": {
     type: "boolean",
     description: "Disable Workspace Trust feature. This switch only affects the current session.",