Update copyright headers

Updating these accurately (especially the start date) is made easier by the helper script introduced in !1549 (merged).

As well as updating existing copyright years for "The Bitcoin developers", this change adds missing "The Bitcoin developers" copyright lines for files that have been modified since the fork from Core, but are only marked for "The Bitcoin Core developers".

Note that there are no erroneous attributions of earlier years to "The Bitcoin developers", thanks to the fork commit cutoff introduced to contrib/devtools/copyright_header.py in !1549 (merged).

Changes exclude the third party libraries.

No functional changes.

Test plan

Examine the git diffs to verify the changes look acceptable. Spot check several files with git log to confirm the newly updated and inserted copyright periods are correct.

ninja check-all to make sure nothing is broken.