Add ':extend t' face attribute to diff faces (bug#37774)

Add ':extend t' face attribute to diff faces (bug#37774)

* lisp/vc/diff-mode.el (diff-header, diff-file-header)
(diff-removed, diff-added): Add ':extend t' face attribute.

* lisp/vc/ediff-init.el (ediff-current-diff-A)
(ediff-current-diff-B, ediff-current-diff-C)
(ediff-current-diff-Ancestor, ediff-even-diff-A)
(ediff-even-diff-B, ediff-even-diff-C, ediff-even-diff-Ancestor)
(ediff-odd-diff-A, ediff-odd-diff-B, ediff-odd-diff-C)
(ediff-odd-diff-Ancestor): Add ':extend t' face attribute.

* lisp/vc/smerge-mode.el (smerge-upper, smerge-lower)
(smerge-base, smerge-markers): Add ':extend t' face attribute.

* lisp/vc/log-view.el (log-view-file, log-view-message):
Add ':extend t' face attribute.

* lisp/faces.el (secondary-selection): Add ':extend t' face attribute.
(line-number-major-tick, line-number-minor-tick):
Change :foreground to :background.