Per AmoebaChant follow-up review feedback: the previous setInteraction
silently mutated the catch-all entry when called with conditions stricter
than any existing entry, which broke unrelated gestures. Example: calling
`setInteraction("pointer", { button: 0, modifiers: { ctrl: true } }, "rotate")`
on the GeospatialCamera default map (which has no ctrl-modifier entry)
mutated the unmodified `{ button: 0, interaction: "pan" }` catch-all and
broke plain left-drag.

New behavior:
- If the matched entry is at least as specific as the supplied conditions,
  mutate its interaction in place (unchanged from before).
- If the matched entry is broader than the conditions (e.g. catch-all
  matched a ctrl-modified request), add a new more-specific entry via
  addEntry instead. The new entry wins for the requested combination
  without clobbering the broader entry.
- If no entry matches at all, also add a new entry.

Internal helpers _entryIsAtLeastAsSpecificAsConditions and
_modifiersAtLeastAsSpecific implement the broader-than detection.

Tests: 5 new cases in cameraMovement.test.ts covering mutate-in-place,
modifier-broader add, button-broader add, no-match add, and the
less-specific-conditions add path. All 189 camera tests pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Collapse _entryIsAtLeastAsSpecificAsConditions and _modifiersAtLeastAsSpecific
into one _entryConstrainsAllOf helper. InputConditions is a flat type with all
source-specific fields optional, so a string-keyed loop over the four fields
(button, key, touchCount, modifiers) covers every source naturally -- the
irrelevant fields for a given source are undefined on both entry and
conditions and harmlessly skip the early return.

Saves ~25 lines, no behavior change. All 5 setInteraction tests still pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The movement system is unconditionally on for ArcRotateCamera (and
GeospatialCamera). The setter has always been a no-op and the getter has
always returned true, so leaving the accessor pair around only added
noise to the public surface and invited misreading of the API.

Soft breaking change: TypeScript users that read or assign
`camera.useMovementSystem` will now see a compile error. Runtime behavior
is unchanged for plain JS users -- writes silently set an instance
property that has no effect (same as before, where the setter no-op'd).

Drops the corresponding 'useMovementSystem backward compat' test block
in arcRotateCameraMovement.test.ts.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>