Interception routes match from nested route navigation (#84898)
### What?
Refactors interception route regex generation to fix nested route
navigation and improve maintainability.
### Why?
Interception routes failed to trigger when navigating from nested
descendant routes. The previous implementation had overly complex,
fragile regex patterns spread across multiple functions that were
difficult to maintain and didn't handle all navigation scenarios
correctly.
The root cause was an overly restrictive header matching pattern
(`/[^/]+` - single segment only) that prevented matching navigation from
deeper nested routes like `/groups/123/settings` → `/groups/123/new`.
### How?
**Simplified Architecture:**
- Consolidated regex generation logic into `route-regex.ts` where it
properly belongs
- Removed ~230 lines of complex, duplicated regex building code from
`generate-interception-routes-rewrites.ts`
- Leveraged existing `getNamedRouteRegex()` with a new `reference`
parameter to handle parameter name mapping
**Parameter Naming Fix:**
- Introduced `nxtI` prefix for parameters adjacent to interception
markers (e.g., `(.)[id]` → `nxtIid`)
- Maintains `nxtP` prefix for regular parameters
- Ensures consistent parameter naming across source, destination, and
regex patterns
**Regex Pattern Fix:**
- Changed header matching from single-segment (`/[^/]+)?` to
multi-segment `(/.+)?` pattern
- Now correctly matches navigation from any descendant route depth
**Test Coverage:**
- Added comprehensive e2e tests for nested navigation scenarios
- Updated existing tests to reflect new parameter naming convention
Fixes #84813
NAR-445
