lazily load typescript for eslint-plugin-svelte3
lazily load typescript for eslint-plugin-svelte3

This drastically decreases run time of the lint job back to an
acceptable level (by about 90%)

yagebu/fava,aumayr/beancount-web,yagebu/fava,aumayr/beancount-web,beancount/fava,beancount/fava,beancount/fava,yagebu/fava,aumayr/beancount-web,yagebu/fava,aumayr/beancount-web,beancount/fava,yagebu/fava,beancount/fava