Fix dap variable value format issue (#90799)

While adding a UI feature in VSCode to toggle hex/dec in variables view
window. I noticed that it does not work after second toggle. Then I
noticed that there is a bug that we only explicitly set hex format not
reset back to default during further toggle. The new test demonstrates
the bug.

This PR resets the format back to default if not using hex. One
complexity is that, we explicitly set registers value format to
AddressInfo, which shouldn't be overridden by default or hex settings.

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Co-authored-by: jeffreytan81 <jeffreytan@fb.com>