Keep GridWrap highlight visible after scroll

[puneetdixit200]

Description:

Fixes #5992

Keeps the GridWrap keyboard highlight clamped to the visible item range after scrolling. This lets subsequent arrow-key navigation continue from the current viewport instead of jumping back to a stale off-screen highlighted item.

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

Testing:

• go test ./widget -run '^TestGridWrap_ScrollKeepsHighlightVisible$' -count=1\n- go test ./widget -run '^TestGridWrap' -count=1\n- go test ./widget -run '^Test(GridWrap|List|Tree)_(ScrollTo|TypedKey|Highlight)' -count=1\n- go vet ./widget\n- go run golang.org/x/tools/cmd/goimports@latest -e -d widget/gridwrap.go widget/gridwrap_test.go\n- go run mvdan.cc/gofumpt@latest -l widget/gridwrap.go widget/gridwrap_test.go\n- git diff --check\n\ngo test ./widget -count=1 hit unrelated local golden-render differences in List/Tree scrollbars/images on macOS; the focused GridWrap and nearby scroll/highlight tests above passed.

[andydotxyz]

I don't agree with this change. Scrolling does not imply the user is not interested in the current selection. See List/Tree etc - the selected item does not change when they scroll.

Selecting an item, then scrolling, then tapping "down" should move to the item below the selected one, not to a new item based on where the viewport is scrolled to

[andydotxyz]

Any other team members want to weigh in on this before I close?