Layer assets are zipped and uploaded by directory.
Layers are unzipped in the /opt dir of Lambda environment.
To properly scope layers, using following structure:

src
 |_ layers
   |_ <layer name>
     |_ nodejs
       |_ <layer name>
         |_ index.ts
         |_ package.json
         |_ ...

This will allow individual layers to be zipped by referencing the
src/layers/<layer name> when creating layer assets.

It will also allow lambda function code to reference layers as packages
scoped to their runtime and prevent filename conflicts when unzipping in /opt:

import * from '/opt/nodejs/<layer name>'