GH-8586: Deprecate IntegrationComponentSpec.get() (#8594)

* GH-8586: Deprecate IntegrationComponentSpec.get()

Fixes https://github.com/spring-projects/spring-integration/issues/8586

The `IntegrationComponentSpec` is not a plain wrapper around single component.
Sometimes it comes with several components where all of them must be registered
as beans.
If `IntegrationComponentSpec.get()` is called from end-user code, we may lose
other related components, for example filters in the `FileInboundChannelAdapterSpec`.

* Deprecate `IntegrationComponentSpec.get()` with no-op for end-user,
rather encourage to leave it as is and let the framework take care about its lifecycle
and related components registration
* Fix `IntegrationComponentSpec` logic to deal as a simple `FactoryBean` instead of
extra overhead via `AbstractFactoryBean`
* Use `IntegrationComponentSpec.getObject()` in the framework code where `get()` was called
* Fix tests to expose `IntegrationComponentSpec` as beans instead of previously called `get()`
* Some other clean up and typos fixes in the affected classes
* Document the change

* * Revert `ObjectStringMapBuilder` in the `KafkaInboundGatewaySpec.getComponentsToRegister()`

* Fix language in docs

Co-authored-by: Gary Russell <grussell@vmware.com>

* * Remove trailing whitespace in the `ScriptMessageSourceSpec`

---------

Co-authored-by: Gary Russell <grussell@vmware.com>

spring-integration-groovy/src/test/groovy/org/springframework/integration/groovy/dsl/test/GroovyDslTests.groovy

@@ -216,7 +216,7 @@ class GroovyDslTests {
 
 		@Bean(PollerMetadata.DEFAULT_POLLER)
 		poller() {
-			Pollers.fixedDelay(1000).get()
+			Pollers.fixedDelay(1000)
 		}