Includes refinements for consistent quoting of names in exception messages.

Issue: SPR-13972

Update SpringFactoriesLoader so that package private classes can be
used.

Issue: SPR-13969

Closes gh-934

Refine the optimizations made in 6f55ab69 in order to restore binary
compatibility and resolve a regression.

Tests of the form pathMatcher.match("/foo/bar/**", "/foo/bar") should
return true as this was the behavior in Spring 4.2.

Issue: SPR-13913

Issue: SPR-13930

Issue: SPR-12857
Issue: SPR-13905

This commit speeds up the AntPathMatcher implementation by
pre-processing patterns and checking that candidates are likely
matches if they start with the static prefix of the pattern.

Those changes can result in a small performance penalty for positive
matches, but with a significant boost for checking candidates that don't
match. Overall, this tradeoff is acceptable since this feature is often
used to select a few matching patterns in a much bigger list.

This will lead to small but consistent performance improvements in
Spring MVC when matching a given request with the available routes.

Issue: SPR-13913

Issue: SPR-13923

Consistent java.util.Optional resolution, lenient handling of optional multipart files, correct Servlet 3.0 Part list/array selection

Issue: SPR-13418
Issue: SPR-13849
Issue: SPR-13850
Issue: SPR-13893

Issue: SPR-12948

Issue: SPR-13344

This change updates all cases where callbacks are invoked to catch and
suppress errors (since there is not match to do with and error from
a callback be it success or failure).

Also updated is the contract itself to clarify this and emphasize the
callbacks are really notifications for the outcome of the
ListenableFuture not the callbacks themselves.

Issue: SPR-13785

Issue: SPR-13858

Issue: SPR-13829

Issue: SPR-13603

Issue: SPR-13828

Issue: SPR-13816

Issue: SPR-13594

Issue: SPR-13758

Issue: SPR-13713

Issue: SPR-13714

Issue: SPR-13685

- Delete unused imports
- Delete unused code
- Clean up warnings

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