Prior to this commit, if a PathContainer was created using
Options.MESSAGE_ROUTE, DefaultPathSegment#parameters() returned a
mutable map which would allow the user to modify the contents of the
static, shared EMPTY_PARAMS map in DefaultPathContainer.

This commit prevents corruption of the shared EMPTY_PARAMS map by
ensuring that parameters stored in DefaultPathSegment are always
immutable.

Closes gh-27064

Closes gh-27058

This commit adds the missing `spring-framework-main-code` asciidoctor
attribute in the reference documentation.

Fixes gh-27041

See gh-27031

Closes gh-27017

Closes gh-27030

Closes gh-27031

See gh-27034

Closes gh-27034

This commit revisits the recently updated `PORT_PATTERN` in
`UriComponentsBuilder`. The fix introduced in gh-26905 fails with
ambiguous URL patterns, especially when the port and path parts of the
pattern are hard to differentiate, for example
"https://localhost:{port}{path}".

This commit reinstates the previous behavior without undoing the actual
fix. The only limitation introduced here is the fact that only a single
pattern variable is allowed for the port pattern part.

Fixes gh-27039

Closes gh-26778

Closes gh-27035

Closes gh-26962

Prior to this commit, the `HttpComponentsClientHttpConnector`
implementation could accept or create a default `HttpClient` instance
but not expose it as part of its API. This effectively prevents
applications from properly closing the associated resources when
disposing of the connector.

This commit implements the `Closeable` interface on the connector to
allow this use case.

Closes gh-27032

Upgrade to Hibernate ORM 5.4.32, RxJava 3.0.13, Aalto 1.3, Gson 2.8.7, Protobuf 3.17.2, XStream 1.4.17, ActiveMQ 5.16.2, HSQLDB 2.5.2, JRuby 9.2.17, Mockito 3.11, HtmlUnit 2.50, Checkstyle 8.43

Closes gh-27023

See gh-26982

Closes gh-26982

Closes gh-27012

Proposed change aimed to keep coherence between variable declaration 
and static initialization code, which stores 9 values, not 8, in these
two maps.

Closes gh-27016

See gh-26989

Closes gh-26987

Prior to this commit, in some cases application context startup steps
could be created concurrently, which could cause issues with the current
implementation tracking the parent/child relationship between steps.

This commit ensures that the flight recorder implementation is using
thread safe collection implementations for that.

Fixes gh-26941

This commit ensures that `DefaultApplicationStartup` returns a static
step for each call to avoid allocations.

Closes gh-26939

Make sure that we use the parameter name in MultipartBodyBuilder::part
when adding a Part, instead of using the name specified in the
'Content-Disposition' header that might have been in the part's headers.

Closes gh-27007