compile with swc for non-watchmode builds

[ryanatkn]

This continues the work started in #45 and adds a new compile task and standalone module that perform one-off builds of the source tree to the build directory. It replaces the usage of the TypeScript compiler in non-watchmode in the two places it makes sense.

So this:

await spawnProcess('node_modules/.bin/tsc');

becomes:

await compile(log);

With this change, Gro's cold startup time in projects with a clean build directory drops dramatically. TypeScript compilation is the large majority of the work performed in that scenario, and this speeds things up by about a factor of 100 on my machine.