Gulp task "copy-cesium-assets" fails in node v12.17.0+

[Stephen Davies]

The error is caused by a change in how node deals with ESM modules. In v12.17.0+ node interprets the exports object in package.json as a complete list of exports for the "terriajs-cesium" package and will fail when other paths are used in a require or import. This trips up our gulp tasks which use require.resolve("terriajs-cesium/package.json") to determine the location of the "terriajs-cesium" package for copying assets etc.

[09:08:28] Starting 'copy-cesium-assets'...
[09:08:28] 'copy-cesium-assets' errored after 2.57 ms
[09:08:28] Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: Package subpath './package.json' is not defined by "exports" in C:\Users\Owner\TerriaMap\node_modules\terriajs-cesium\package.json
    at applyExports (internal/modules/cjs/loader.js:491:9)
    at resolveExports (internal/modules/cjs/loader.js:507:23)
    at Function.Module._findPath (internal/modules/cjs/loader.js:635:31)
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:953:27)
    at Function.resolve (internal/modules/cjs/helpers.js:78:19)
    at C:\Users\Owner\TerriaMap\node_modules\terriajs\gulpfile.js:78:33
    at copy-cesium-assets (C:\Users\Owner\TerriaMap\node_modules\undertaker\lib\set-task.js:13:15)
    at bound (domain.js:426:14)
    at runBound (domain.js:439:12)
    at asyncRunner (C:\Users\Owner\TerriaMap\node_modules\async-done\index.js:55:18)

To fix this problem:

• Merge TerriaJS/cesium#73
• Release "terriajs-cesium"
• Release terriajs master pointing to new package version
• Update TerriaMap master
• Release terriajs next pointing to new package version (blocked on #4386)
• Update TerriaMap next