Forms, a11y · Checkbox, Switch, Radio, RadioGroup, Slider and Select name their role, label and state (#3)

A slider's thumb reports its value, the bounds it can reach and its orientation; a select's trigger its value, placeholder and whether its list is open; a disabled control says so in its description.

tasks/github.md

@@ -2,5 +2,5 @@
 
 - [x] G1 PR #1: build on Windows with `escape_args`; review, verify, merge, answer CodeRabbit
 - [x] G2 Issue #2: tree guides line up under the chevron and run unbroken across rows
-- [ ] G3 Issue #3: Checkbox, Switch, Radio, Slider and Select name their role, label and state
+- [x] G3 Issue #3: Checkbox, Switch, Radio, Slider and Select name their role, label and state
 - [ ] G4 Push, comment on #2 and #3, close #2