Create a list of compiler/cargo features desired to be stabilized/implemented for embedded use cases

[manczak-ifx]

As discussed in the Unconf Rustweek2025 a list of features for the compiler that are necessary for embedded use cases (e.g. security extensions) and cargo features (e.g. support of multiple runners, workspaces with multiple targets)

[BartMassey]

We haven't made any progress. Should probably discuss in an REWG meeting soon.