Add forgotten modules to std.package.

[berni44]

Maybe typetuple was intentionally left out?

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[Herringway]

std.outbuffer, std.typetuple and std.xml were intentionally removed by #6889 (std.typetuple was commented out already, however).

[berni44]

std.outbuffer, std.typetuple and std.xml were intentionally removed by #6889 (std.typetuple was commented out already, however).

Then it's only about adding sumtype. :-)