[theia-dev] We now use npm to build Theia

[Thomas Mäder <t.s.maeder@xxxxxxxxx>]

Hi folks,

I've just merged https://github.com/eclipse-theia/theia/pull/14481, which changes our code base to use "npm" instead of "yarn" to build the code in https://github.com/eclipse-theia/theia. All other repos and generators remain unchanged. 

 If you are an adopter of Theia and you consume the Theia packages from the npm registry, this change should not affect you at all. Please report issue if there any problems with building Theia-based applications.

If you do build Theia from source, the documentation at https://github.com/eclipse-theia/theia/blob/master/doc/Developing.md should be up to date and working. Please report any issues. Some of the root package.json scripts have changed, so please have a look. If you encounter any problems, please file bugs ASAP. This is a major change so some breakage is likely and would ideally be fixed before the next release.

There is currently an issue in npm with version overrides: https://github.com/npm/cli/issues/5850. So if you are updating package-lock.json, make sure that the packages from the overrides are still at the appropriate version. 

regards, Thomas