Add Dragon/Skyriding Support to Movement Speed Datatext

[Bauxite]

Troubleshooting Steps

Describe the expected behavior and what actually happened?

The GetUnitSpeed API does not return real values while Dragon(Sky)riding, but the IsFlying API does return true. so the Movement Speed datatext returns the maximum steady flying speed. The GetGlidingInfo API's return values of isGliding / forwardSpeed can be used instead to display proper values while Dragon(Sky)riding.

local function DelayUpdate(self)
    local _, runSpeed, flightSpeed, swimSpeed = GetUnitSpeed('player')
    local isGliding, canGlide, forwardSpeed = C_PlayerInfo.GetGlidingInfo()

    local speed

    if isGliding then
        speed = forwardSpeed
        wasFlying = true
        elseif IsSwimming() then
        speed = swimSpeed
        wasFlying = false
       ...

Reproducing the issue.

• Mount a dragonriding mount in retail
• The Movement Speed datatext reads at 210% while grounded (assumes Mount Up guild perk and no other modifiers)
• The Movement Speed datatext reads at 420% while flying (assumes Mount Up guild perk and no other modifiers)

Lua Errors

N/A

Verification Steps

• [X] I have read the Changelog and verified ElvUI is up to date by checking /estatus
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• [X] I have done the Troubleshooting Steps and included the requested screenshots, which show the issue and status panel.