[devtools] Fix indicator dragging on touch screens (#97723)
### What?
- Restore `touch-action: none` on the draggable devtools indicator.
- Add integration coverage for the draggable computed touch action.
### Why?
PR #86816 made devtools content selectable, but also removed
`touch-action: none` with the selection styles. On touch screens, that
allows the browser to claim the gesture for viewport panning and
suppress the pointer event stream, causing the indicator to stop moving.
### How?
Keep the drag-lifecycle selection handling introduced by #86816 and
restore only `touch-action: none` before the gesture begins.
Fixes #97668
### Testing
- `pnpm build --filter next`
- Targeted Prettier and ESLint checks
- `NEXT_SKIP_ISOLATE=1 pnpm test-dev
test/development/app-dir/devtools-position/default-position.test.ts`
