[DDC] Replace amd module system by ddc module system

[annagrin]

We currently use require.js module system (that implements the AMD API) in flutter and webdev, but AFAIK it is not currently maintained (latest release., 2.3.6, was in 2018)

DDC module system is faster and more flexible for our use (allows implementing new features like multi-app debugging, lazy build, hot restart, clearing the statics etc).

There are also some issues with require.js that would be solved by the move. Will attach the issues as we go to understand priority.

Work needed (approximately):

• DDC

  • make sure tests run with DDC module system
  • move DDC library loading code and bootstrap & html generator to dart SDK repo
  • provide helpers for bootstrap generation
    • update builds - frontend server, build_web_compilers, blaze.

• Flutter tools

  • use DDC module system when running frontend server
  • update bootstrap code

• build_web_compilers

  • use DDC module system for compilation
  • update bootstrap code

• DWDS

  • remove support for amd module system