Support for the new runtime feature "default theme"

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

Since SAP/openui5@01e9de75c, the UI5 runtime supports a so called default theme. If an application configures no theme at all, no longer the incomplete base theme is used, but a default theme which depends on the used UI5 version. This feature has not only been added in master, but also in all older maintenance branches.

However, during development, one always has to reference a concrete theme project in the ui5.yaml's framework section . It's not yet possible to omit this and let the tooling pick the right dependency.

Describe the solution you'd like

It would be nice if one could specify the use of the default theme also in the dependencies of a project, either

• by a 'magic' dependency name (like themelib_sap_default) which the tooling then translates into the default theme of the referenced UI5 version
• or by omitting theme libs in the framework section and rather specifying a dedicated configuration (e.g. useDefaultTheme: true).

Describe alternatives that you've considered

Using the CDN is an alternative as the CDN always contains the necessary default theme per version. But this would limit the use of the default-theme feature.

Relevance

As changes of the default theme are not that frequent in UI5, this is not a hot topic. Nevertheless, support for default themes feels a bit incomplete without it.

No file or test is named in the issue. Start by tracing how UI5 CLI reads framework dependencies and resolves theme projects, then compare that flow with the default-theme behavior introduced in SAP/openui5@01e9de75c; done means a project can select the version-appropriate default theme without naming a concrete theme library.