fix(ui): correctly apply iOS safe area padding when using q-tabs

[yusufkandemir]

What kind of change does this PR introduce?

• Bugfix

Does this PR introduce a breaking change?

• Maybe: if the users patched the safe area themselves because the builtin solution wasn't working, this might break their apps depending on the element they applied padding

The PR fulfills these requirements:

• It's submitted to the dev branch (or v[X] branch)

Other information:
.q-tabs-head seems to be left from v0.17, it's now .q-tabs__content

.q-tabs:last-child doesn't work when using the elevated prop of q-footer, as the last child of the footer becomes the layout shadow div. So, fortified the selector to work regardless of whether the footer is elevated or not.