Issue: SPR-14711

* pr/1292:
  Polish
  Polish contribution
  Honour ErrorHandler if `Cache.put` fails

Closes gh-1292
Issue: SPR-15188

This commit makes sure that the `ErrorHandler` is invoked if the cache
fails to put an element (be it in the main cache or the exception cache).

See gh-1292
Issue: SPR-15188

This commit introduces the RenderingResponse, a template
rendering-specific subtype of ServerResponse that exposes model and
template data.

* pr/1311:
  Polish javadoc

Closes gh-1311

* pr/1312:
  Polish javadoc

Closes gh-1312

The base URI is ignored for requests that include a host.

WebClient exposes UriBuilder (rather than UriBuilderFactory) for
per-request URI building based on the base URI. That provides
full control to add or replace components of the base URI.

Leave only one static, no-arg build() method for access to a Builder.

URI-related preferences are now exposed on the builder itself.

Improve Javadoc with base URI examples.

Issue: SPR-15210

Issue: SPR-15212

Issue: SPR-15214

Issue: SPR-15215

Issue: SPR-15216

Issue: SPR-14998

Issue: SPR-15190

Issue: SPR-15190

Issue: SPR-15190

Issue: SPR-15208

This commit makes the following changes:

 - Merge WebClient into ExchangeFunction. Static methods on WebClient
have been moved to the utility class ExchangeFunctions, similar to
RouterFunctions operates on the server side.

 - Renamed WebClientOperations to WebClient.

 - Renamed WebClientStrategies to ExchangeStrategies

Issue: SPR-15131

Remove the use of SocketUtils#findAvailableTcpPort in favor of letting
servers pick a dynamic port by specifying port 0.

This commit removes the use of SocketUtils#findAvailableTcpPort in
favor of letting servers pick a dynamic port by specifying port 0.

This should make integration tests more stable because the port is
chosen at the place where it needs to be used. It gives servers a
chance to try to open a socket on some port and start using the socket
if successful.

Issue: SPR-15200

Issue: SPR-15135

Issue: SPR-15158

Issue: SPR-15202

Issue: SPR-15196