[Package] Add script to package up assembleVegaLite() functionality for use in peer projects

[Alper Sarikaya (yelper)]

Adds (Copilot-generated) script to generate a *.tgz npm package so that functionality can be imported in peer projects. This "flint-chart-compiler" project only exports the assembleVegaLite() function and associated functionality/types.

Trigger a build by changing the version in "compiler.package.json", then running the following script:

npm run pack:compiler
# → produces microsoft-flint-chart-compiler-0.1.0.tgz

Copy the tarball to the repository wanting to use the functionality, and import the package as a dependency:

pnpm add microsoft-flint-chart-compiler-0.1.0.tgz

Once the package is added, then the package can be referenced by name in that respository, e.g.:

import { assembleVegaLite } from '@microsoft/flint-chart-compiler';
import type { ChartAssemblyInput } from '@microsoft/flint-chart-compiler/core';

Once we figure out publishing to npm by going through the Microsoft open-source process, peer repositories can just add the dependency by name.