feat: to be able to disable systemjs in build

[LiKang6688]

Motivation

it takes too much time to build an extension using nebula build

solution

Add systems into config to be able to disable systemjs build

systemjs: {
    description: 'Enable to transpile a systemjs format for release',
    type: 'boolean',
    default: true,
  },

argv.systemjs && (await systemjs(buildConfig));

Usage example

qlik-oss/sn-table#991

One more thing:

Refactoring build/lib to separate related functions to its own file

Requirements checklist

• Api specification
  • Ran yarn spec
    • No changes OR API changes has been formally approved
• Unit/Component test coverage
• Correct PR title for the changes (fix, chore, feat)

When build and tests have passed:

• Add code reviewers, for example @qlik-oss/nebula-core