[rollup-plugin] Cache npm modules after first rollup execution

[muenzpraeger]

Is your feature request related to a problem? Please describe.
If npm modules are used that expose additional LWCs (like lwc-components-lightning) every rollup execution in watch mode runs an exhaustive search across all npm modules. While it's necessary for the initial launch this step could be optimized for subsequent runs.

Describe the solution you'd like
The module search in installed npm modules should happen only once, and then use a cache.

Possible solution
If rollup runs in watch mode the first run of @lwc/module-resolver should cache the search results (i. e. as node_modules/.cache/lwc-modules-resolved.json.