Public data for DFUFirmware

[NickKibish]

Purpose:

I need have an access to DFUFirmware data. It's required for my Flutter version of DFU library. @philips77 Do yo have any objections regarding adding computed value from DFUStream?

[CLAassistant]

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[philips77]

What do we do with that PR? Do you still need it or someone else would?

[philips77]

I'm closing the PR. If needed for someone, we can always reopen it.

[Crudough]

@philips77 I also need to expose this data. Requesting to re-open this PR. Thanks!