Issue: SPR-13801

In several places in the spring-webmvc module, URL patterns / objects
relationships are kept in `HashMap`s. When matching with actual URLs,
the algorithm uses a pattern comparator to sort the matching patterns
and select the most specific. But the underlying collection
implementation does not keep the original order which can lead to
inconsistencies.

This commit changes the underlying collection implementation to
`LinkedHashmap`s, in order to keep the insert order if the comparator
does not reorder entries.

Issue: SPR-13798

Issue: SPR-13791

Before this change the compilation of a method reference or property/field
access was not properly cleaning up the stack if compilation meant
calling a static method or accessing a static field. In these cases there
is no need for a target object on the stack and it should be removed if
present. For a simple expression it is harmless since the end result of
the expression is the thing on the top of the stack, but for nested
expressions if the inner expression suffered this issue, the outer
expression can find itself operating on the wrong element.

The particular issue covered the case of a static field access but this
fix (and associated tests) cover static method, property and field access.

Issue: SPR-13781

Base64Utils: URL/File Safe Alphabet

Issue: SPR-13784

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-13757

Issue: SPR-13704

Issue: SPR-13783

Issue: SPR-13782

Issue: SPR-12926

Issue: SPR-13776

Issue: SPR-13746

Issue: SPR-13769

Issue: SPR-13774

Issue: SPR-13772

Issue: SPR-13696