Well.. in the meantime, I built the def types myself. I don't find a way of doing this with esbuild, so I did my own script for generating them. The main goal is getting the spine-phaser types but I hope it also works for spine-core and spine-webgl. The *.d.ts files are in the dist/ folder.
https://github.com/PhaserEditor2D/spine-phaser-iief-types/
