Add support for flat build output of the root (library-)project

[RandomByte]

Is your feature request related to a problem? Please describe.

Many target platforms for UI5 projects expect a "flat" directory structure to be deployed. Meaning that there is no resources/ directory and no my/company/project namespace structure.

Explanation: Such projects might be deployed to different endpoints (i.e. they might not share a relative path). At UI5 runtime they are then loaded by configuring the corresponding resource mapping. This makes it unnecessary or even confusing in some cases to have another UI5 runtime-oriented directory structure below the project's deployment endpoint.

Describe the solution you'd like

This behavior is already in place for application projects. But it's missing for library and theme-library projects and the expected behavior for component projects is yet to be decided.

There are already multiple solutions available:

• SAP Web IDE executes a "flatten" script after every build which uses the cp and rm UNIX commands
• There's a custom task "ui5-task-flatten-library"

Since this is a very common use case and the basic functionality is already present in UI5 Tooling thanks to the ui5-fs abstraction layer, it might make sense to have this as a standard offering of UI5 Tooling itself.

Solution proposals

A solution might be to offer a CLI flag which always flattens the root project of the build.

An alternative would be to always flatten the root project if no other projects are being built (i.e. no --all build).

Describe alternatives you've considered

See existing solutions above

Additional context

none