Update spdlog

[rzhao271]

This PR updates the spdlog submodule to v1.8.5, and fixes our code where needed.

• We now have an initThreadPool method rather than a setAsyncMode method.
• The implementation of the VoidFormatter has also changed.

Affects microsoft/vscode#121513

I tested my changes by running npm rebuild and then npm run test using node v15.14.0. I did not use electron-rebuild, because I couldn't find a way to issue npm run test commands after running it; I'd get messages like

Error: The module '/Users/raymondzhao/work/node-spdlog/build/Release/spdlog.node'
was compiled against a different Node.js version using
NODE_MODULE_VERSION 88. This version of Node.js requires
NODE_MODULE_VERSION 83.

if I used electron-rebuild or node v14.16.0.

Maybe this means that the spdlog submodule has to somehow be rebuilt with the right version of node, though I'm not sure how.

[deepak1556]

Once you have built for electron you need to use ELECTRON_RUN_AS_NODE=1 electron.exe <path-to-mocha-binary>

[rzhao271]

That worked! All the tests are still passing.

[gabime]

In spdlog 1.x calling init_thread_pool(..) is not enough to make the loggers async. see https://github.com/gabime/spdlog/wiki/6.-Asynchronous-logging#creating-async-loggers

[deepak1556]

Also needs change to implement the new way of creating async loggers as mentioned by @gabime

[rzhao271]

A few changes

• The loggers are single-threaded
• The only function that creates a logger, other than new spdlog.Logger(), is createRotatingLogger()
• I've exported the shutdown() function https://github.com/gabime/spdlog/wiki/6.-Asynchronous-logging#windows-issues and a flushEvery() function.

[rzhao271]

Due to microsoft/vscode#121852, I'll add another function that creates a synchronous logger during debt week.

[gabime]

switch back to using _mt loggers, since the flushing requires thread-safe loggers to work

Actually _mt is not required if the sinks are used only in async logger(and as long the thread was pool has single thread).

[deepak1556]

Thanks for the context @gabime, have confirmed with @rzhao271 that vscode uses the sync logger and async logger from different processes so it is safe to use the _st version.