feat(a380x): allow vertical revision in alternate and fix waypoint selection logic

[BravoMike99]

Fixes #10617

Summary of Changes

Adds STEP ALTs page access restrictions.
Adds SPD/ALT constraints revision at the alternate.
Adds automatic waypoint selection upon navigation to the ALT/SPD CSTR page, if nothing was selected prior.

Screenshots (if necessary)

References

Additional context

Discord username (if different from GitHub): bruno_pt99

Testing instructions

Check that the SPD/ALT cstr page works ok and that you can modify constraints in waypoints of the alternate flight-plan as well as ones in the active.
Check that you get a STEP ALTS NOT ALLOWED: when attempting to access the page after top of descent for example.
Check that the assigned issue no longer occurs when you click the SPD CSTR after the cruise phase.
Check that STEP ALTs page works as usual.

How to download the PR for QA

Every new commit to this PR will cause new A32NX and A380X artifacts to be created, built, and uploaded.

1. Make sure you are signed in to GitHub
2. Click on the Checks tab on the PR
3. On the left side, find and click on the PR Build tab
4. Click on either flybywire-aircraft-a320-neo, flybywire-aircraft-a380-842 (4K) or flybywire-aircraft-a380-842 (8K) download link at the bottom of the page