fix(380x/fg): limit managed speed by characteristic speeds

[BravoMike99]

Fixes #[issue_no]

Summary of Changes

Constraints the target managed speed by the flight guidance based on the characteristic speed of the current flap lever position.

Screenshots (if necessary)

References

Additional context

Discord username (if different from GitHub): bruno_pt99

Testing instructions

Program a constraint below your green-dot speed, takeoff and retract the flaps.
Observe how the FD/AP targets the green dot speed rather than the constraint.
During approach, check that the managed speed target does not go below green-dot, S speed etc (appropriate characteristic speed for the current configuration).
No changes to the guidance are expected otherwise.

How to download the PR for QA

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