VideoBackends: Allow the viewport to use the full depth range.

[CrossVR]

Some games have a huge depth range, normally we would clamp the depth value, but that's not possible with fast depth. So instead we intelligently clamp the depth range to a small part of the full depth range.

[dolphin-emu-bot]

FifoCI detected that this change impacts graphical rendering. Here are the behavior differences detected by the system:

• chibi-robo-zfighting on ogl-lin-mesa: diff
• nfsu-reflections on ogl-lin-mesa: diff
• smg2-fog on ogl-lin-mesa: diff
• sw3-dt on ogl-lin-mesa: diff
• tos-invis-char on ogl-lin-mesa: diff

_{^{automated-fifoci-reporter}}

[JMC47]

Tony Hawk is still broken on slow-depth, Sonic The Fighters is still broken on fast depth.

[degasus]

LGTM