XWIKI-10536: Capitalize first letter for buttons when adding a tag.

* Fix failing tests.

(cherry picked from commit b15e02b9613db944965bf6bbe64b8d7b18a6c36f)

Conflicts:
	xwiki-platform-core/xwiki-platform-tag/xwiki-platform-tag-test-pageobjects/src/main/java/org/xwiki/tag/test/po/AddTagsPane.java

(cherry picked from commit 5eaf298dc76e549a361d6f7aa293361d481f0b10)

Conflicts:
	xwiki-platform-core/xwiki-platform-tag/xwiki-platform-tag-test-pageobjects/src/main/java/org/xwiki/tag/test/po/AddTagsPane.java