Bumping versions to 17.3.0.

[RoyalPineapple]

Cuts the 17.3.0 release for the isSelectable change in #623. Bumps LISTABLE_VERSION to 17.3.0 and moves the isSelectable entry from the Main section of the changelog into a dated 17.3.0 section.

Release notes

Added

• Added isSelectable to ApplyItemContentInfo, reflecting whether the item's selectionStyle is interactive (.tappable, .selectable, or .toggles). ItemContent implementations can read this to represent themselves as interactive, for example by applying the .button accessibility trait so VoiceOver users know the item responds to taps.

Notes

• Docs were not regenerated in this PR: Scripts/generate_docs.sh hangs during sourcekitten parsing under the local Ruby 3.2.2 toolchain (the same environment issue noted in the 17.2.0 bump, Bumping versions to 17.2.0. #622). Docs can be regenerated in a follow-up under Ruby 3.3.x.

Checklist

Please do the following before merging:

• Ensure any public-facing changes are reflected in the changelog. Include them in the Main section.