Support grouping of registers

[jreineckearm]

In GDB, registers can be categorized by groups.
Groups and their registers can be announced as part of the target description XML, see bottom of: https://sourceware.org/gdb/current/onlinedocs/gdb.html/Target-Description-Format.html There are predefined groups, but also custom grouping is handled.

Depending on the number of registers to display, it can become tedious to navigate through them in the Variables window.
I'd propose to group registers and display a tree accordingly to make navigation more efficient.

[jreineckearm]

Not as straight forward as originally expected. The target XML descriptions are part of the gdb remote protocol, not the gdb MI protocol. Groups are not easily accessible there.

It might be possible to extract the information by sending maintenance commands. But response are not structured MI, hence would need additional parsing action and potentially dropping related output events.

May have to pause this due to other priorities.