The functionality to frame channels in the Graph Editor
did not take into account any NLA mapping, causing the
viewport to frame the wrong part.
Fix it by mapping the `rctf` x-values
I had to remove the `const` on a parameter from the function
since `ANIM_nla_mapping_get` doesn't take a `const`.
Pull Request: https://projects.blender.org/blender/blender/pulls/114325