In order to make `GeoShapeUtil.configure()` actually ignore colliding
`customGeoTypes` keys, this PR strips the colliding entries out of the
options before delegating to `super.configure()`. Follow-up to review
feedback on #8705.

Previously, the dev-mode warning said the colliding key would be
ignored, but only the schema registration was skipped. The colliding
entry still landed in `this.options.customGeoTypes` and was consulted at
runtime in three places that silently changed built-in behavior:

- `toolStates/Pointing.ts` — used the user's `defaultSize` for built-in
geos when drag-creating with no drag.
- `DefaultStylePanelContent.tsx` — filtered the built-in style panel
item out (`STYLES.geo.filter((item) => !customGeoTypes?.[item.value])`)
and replaced its icon.
- `GeoShapeUtil.onDoubleClick` — ran the user's handler on the built-in
geo.

Now the warning matches reality: colliding entries are dropped from the
options object that's stored on the util.

### Change type

- [x] `bugfix`

### Test plan

1. Run the new tests in `GeoShapeUtil.test.tsx`
(`describe('GeoShapeUtil.configure with customGeoTypes')`).

- [x] Unit tests

### Release notes

- Fix `GeoShapeUtil.configure()` so colliding `customGeoTypes` keys are
actually ignored, instead of leaking through to the tool's default size,
the style panel, and the double-click handler.

### Code changes

| Section   | LOC change |
| --------- | ---------- |
| Core code | +11 / -5   |
| Tests     | +51 / -0   |


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### Change type

- [ ] `bugfix`
- [ ] `improvement`
- [ ] `feature`
- [ ] `api`
- [x] `other`