Make proto-loader-gen-types callable.

[sjohnsonaz]

Is your feature request related to a problem? Please describe.

I would like to call proto-loader-gen-types from TypeScript code. However, nothing is exported.

Describe the solution you'd like

Add export to writeAllFiles() so that it can be called directly.

It is located in the file:

/packages/proto-loader/bin/proto-loader-gen-types.ts

Describe alternatives you've considered

I am currently calling exec(), but this is not ideal.

Additional context