fix(next): custom views not overriding built-in single-segment routes (#14066)

### What?

Fixes the ability to override built-in single-segment admin views (like
`create-first-user`, `login`, `account`, etc.) with custom views via
`admin.components.views`.

### Why?

Previously, when users tried to replace built-in views like
`create-first-user` using the custom views configuration, the built-in
view would still render. The routing logic in `getRouteData.ts` was
checking for built-in views before checking for custom view overrides,
making it impossible to replace them.

### How?

Modified the route matching logic in `getRouteData.ts` to check for
custom view overrides before falling back to built-in `oneSegmentViews`.
When a custom view is configured with a key matching a built-in view
(e.g., `'create-first-user'`), the custom view now takes precedence
while preserving the correct template type and view type from the
built-in configuration.

Fixes #14046