message: getting rid of imodeljs-native aggregator packages
diff: "//dependencies": [
  "NOTE: these dependencies are specific to imodeljs-backend",
  "NOTE: these dependencies should be only for things that DO NOT APPEAR IN THE API",
  - "NOTE: backend directly depends on the node and electron addons as a help to apps. Most apps by far will use one",
  - "or the other of these addons. And, most apps will be installed by npm. So, by putting these dependencies here, we can ",
  - "relieve most apps of the burden of even thinking about 'the addon'. In fact, the addon is not really separate from",
  - "imodeljs-backend but is just part of its internal implementation. We want apps to think about backend, not the addon.",
  "NOTE: While, imodeljs-native-platform-api seems like it should be a devDependency, it is actually required at run time.",
  "The NativePlatformRegistry reads it in order to learn what API was used to compile backend. (Also, if we don't make it a real dependency here, then ",
  - "apps would have to depend on it, as imodeljs-native-platform-node has a peerDependency on it.",
  - "NOTE: These dependencies do not suffice to supply the imodeljs-backend or testbed unit tests with the addons that they need.",
  - "*** Keep this in synch with nativePlatformForTests ***"
  + "apps would have to depend on it, since this package has a peerDependency on it.",
  + "*** Keep this in synch with tools/native-platform-installer ***"
  ],
  "dependencies": {
  "@bentley/imodeljs-native-platform-api": "~19.2.0",
  - "@bentley/imodeljs-native-platform-node": "~19.2.0",
  - "@bentley/imodeljs-native-platform-electron": "~19.2.0",
  "fs-extra": "^6.0.1",
  "js-base64": "^2.4.0",
  "glob": "^7.1.2"
  },
  "//optionalDependencies": [
  - "NOTE: Rush (as of 4.2.5) does not support optionalDependencies!"
  + "NOTE: Rush (as of 4.2.5) does not support optionalDependencies!",
  + "NOTE: These optionalDependencies are here as a help to apps. Most apps by far will use one",
  + "or the other of these addons. And, most apps will be installed by NPM, not rush. So, by putting these dependencies here, we can ",
  + "relieve most apps of the burden of even thinking about 'the addon'. In fact, the addon is not really separate from",
  + "imodeljs-backend but is just part of its internal implementation. We want apps to think about backend, not the addon.",
  + "NOTE: These dependencies do NOT suffice to supply the imodeljs-backend unit tests with the addons that they need.",
  + " Unit tests must rely on tools/native-platform-installer to supply them with the addons they need.",
  + "*** Keep this in synch with tools/native-platform-installer ***"
  ],
  + "optionalDependencies": {
  + "@bentley/imodeljs-n_8-darwin-x64": "~19.2.0",
  + "@bentley/imodeljs-n_8-linux-x64": "~19.2.0",
  + "@bentley/imodeljs-n_8-win32-x64": "~19.2.0",
  + "@bentley/imodeljs-e_2-win32-x64": "~19.2.0"
  + },
  "nyc": {
  "include": [
  "./src/**/*.ts"
  