v0.12.6

• Add debug validation of capture only property use in widgets that don't capture it.
• Fix Wayland custom chrome breaking window padding.
• Fix window text properties affecting the Wayland fallback chrome text.
• Fix swgl build error.
• Changed how relative lengths are computed in offset, x and y, now uses the maximum bounded length from constraint, the same as size properties.
• Fix display print of FactorPercent not rounding.
• ChildInsert::{Over, Under} now allows insert to affect layout size, like other inserts.
  • Use background and foreground properties as layout passive alternatives for child_under and child_over.
• Add zng::container::child.
• Breaking zng_wgt_container::child can now be used as a standalone property that behaves the same as child_under.
  • Note that this is only a breaking change for direct dependents of zng-wgt-container.
• Fix warning on flood with 0 area.
• Add zng::task::Progress value type for reporting a task progress status.
• Add zng::progress with ProgressView widget for displaying a task progress status.