* lisp/tab-bar.el: Rename args to consistent naming convention.

* lisp/tab-bar.el: Rename args to consistent naming convention.

Use the same naming scheme for function arguments.  Use the term "index" when
arguments count from 0, and the term "number" when arguments count from 1.

* lisp/tab-bar.el (tab-bar-select-tab): Rename ‘arg’ to ‘tab-number’.
(tab-bar-move-tab-to): Rename ‘from-index’ to ‘from-number’
and ‘to-index’ to ‘to-number’.
(tab-bar-move-tab-to-frame): Rename ‘from-index’ to ‘from-number’
and ‘to-index’ to ‘to-number’.
(tab-bar-new-tab-to): Rename ‘to-index’ to ‘tab-number’.
(tab-bar-close-tab): Rename ‘arg’ to ‘tab-number’
and ‘to-index’ to ‘to-number’.
(tab-bar-rename-tab): Rename ‘arg’ to ‘tab-number’.
(tab-bar-change-tab-group): Rename ‘arg’ to ‘tab-number’.