Allow specifying tsserver NODE_ENV --max-old-space-size via config variable

[seankwalker]

Hey there, longtime tsuquyomi user here! Thank you for such a wonderful plugin 🙏 When working on larger projects, I noticed that using various commands (e.g. jump to definition, show hint) would make vim hang for a long time, with tsserver evidently struggling. With some hacking, I realized that bumping the --max-old-space-size of the node process running tsserver seemed to help with this.

This PR exposes config variable tsuquyomi_tsserver_max_old_space_size to allow the user to easily configure the heap size for the node process running tsserver.

There's no open issues for this or anything, but it's helped save me some time so figured I'd open a PR to see if there's any interest in getting this in mainline. Thanks!

** the Japanese in the docs was translated by GPT-4o so please forgive any mistakes