Issue: SPR-14349
(cherry picked from commit ca12e13e)

Issue: SPR-14345
(cherry picked from commit d51c22a7)

Issue: SPR-14257
(cherry picked from commit 24f5f368)

Issue: SPR-14298
(cherry picked from commit a979885d)

Issue: SPR-14211
(cherry picked from commit bf7b4752)

Issue: SPR-14209
(cherry picked from commit 9bf5a5cb)

(cherry picked from commit 537193a4)

Issue: SPR-14056
(cherry picked from commit 35eb52e5)

Issue: SPR-14089
(cherry picked from commit 3910350b)

(cherry picked from commit 9af12d29)

Issue: SPR-14067
(cherry picked from commit ec7c3aa3)

Issue: SPR-13981
(cherry picked from commit 7a32ce31)

(cherry picked from commit 028a6901)

(cherry picked from commit ca19920d)

(cherry picked from commit 1899fb37)

Issue: SPR-13923
(cherry picked from commit 449f7046)

(cherry picked from commit e9031061)

Issue: SPR-13858
(cherry picked from commit 5d4547d3)

(cherry picked from commit 27c2e8c8)

Issue: SPR-13829
(cherry picked from commit aecb8b6c)

Issue: SPR-13713
(cherry picked from commit f8860e29)

Issue: SPR-13791

JIRA: https://jira.spring.io/browse/SPR-13784

JDK8 and Apache Commons Codec support the RFC 4648
"URL and Filename Safe" Base64 alphabet.

Add methods to `Base64Utils` to support this feature.

Issue: SPR-13783

Issue: SPR-13696

Issue: SPR-13755

This commit reworks the arrangement to a centralized cache, avoiding any extra reflection attempts if a cache entry is known already. In the course of this, it also enforces toXXX methods to be declared as non-static now (which is the only sensible arrangement anyway).

Issue: SPR-13703

Issue: SPR-12926