Tracking issue for `braced_empty_structs` (RFC 218)

[aturon]

Allows empty structs using braces, as per rust-lang/rfcs#218. This issue tracks stabilization.

[petrochenkov]

Need to land #29383 and fix #29548 before stabilizing

[petrochenkov]

I'd like to have this stabilized in this cycle.
#29548 can actually be fixed in much cleaner way if the feature gate is removed, so I suggest to remove it sooner and not in the end of the cycle.

[petrochenkov]

I can't ping @rust-lang/lang, so ping @aturon

[alexcrichton]

cc @rust-lang/lang (yay github permissions?)

[alexcrichton]

triage: I-nominated

[aturon]

The lang team is moving this feature into final comment period. 🎱

[aturon]

The lang team has decided to stabilize this feature.