The Spring portfolio is changing to use <inception-year>-present in
the copyright headers to simplify keeping headers up to date. This
commit updates the headers and the checkstyle accordingly.
The commit updated etc/checkstyle/header.txt
It also updated the copyright headers using the following find/replace:
Find: (Copyright \d{4})\s*(\-\d{4})? the original author or authors.
Replace: Copyright 2004-present the original author or authors.
Closes gh-17633
