Proposed API checks fail due to nullExtensionDescription when symlinks (`npm link`) is used (doc needed?)

<!-- ⚠️⚠️ Do Not Delete This! bug_report_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- 🕮 Read our guide about submitting issues: https://github.com/microsoft/vscode/wiki/Submitting-Bugs-and-Suggestions --> <!-- 🔎 Search existing issues to avoid creating duplicates. --> <!-- 🧪 Test using the latest Insiders build to see if your issue has already been fixed: https://code.visualstudio.com/insiders/ --> <!-- 💡 Instead of creating your report here, use 'Report Issue' from the 'Help' menu in VS Code to pre-fill useful information. --> <!-- 🔧 Launch with `code --disable-extensions` to check. --> Does this issue occur when all extensions are disabled?: No <!-- 🪓 If you answered No above, use 'Help: Start Extension Bisect' from Command Palette to try to identify the cause. --> <!-- 📣 Issues caused by an extension need to be reported directly to the extension publisher. The 'Help > Report Issue' dialog can assist with this. --> - VS Code Version: ``` Version: 1.57.0-insider Commit: 1082913dd012e21cc5f35a06f15c480ca447f67f Date: 2021-05-27T06:55:34.773Z Electron: 12.0.9 Chrome: 89.0.4389.128 Node.js: 14.16.0 V8: 8.9.255.25-electron.0 OS: Linux x64 5.10.28-1rodete1-amd64 ``` - OS Version: Debian-derived (non-public) Use case here is wanting to modify an extension + an npm package it depends on. In my case, modified vscode-clangd extension with modified vscode-languageclient package. Steps to Reproduce: 1. Clone extension ([vscode-clangd](https://github.com/clangd/vscode-clangd)) and library ([vscode-languageserver-node](https://github.com/microsoft/vscode-languageserver-node)) and install dependencies. 2. Link vscode-clangd to the checked-out vscode-languageclient in the vscode-languageserver-node repo: `cd ~/src/vscode-languageserver-node/client; npm link; cd ~/src/vscode-clangd; npm link vscode-languageclient`. This creates a symlink `~/src/vscode-clangd/node_modules/vscode-languageclient --> ~/src/vsc…