Introduce LocaleResolver for RESTEasy Reactive

[geoand]

Fixes part of #19171

[gsmet]

Ah, cool, thanks. Totally forgot about this feature!

[geoand]

That's better than me, I never knew about it :)

[quarkus-bot]

Failing Jobs - Building a530db1

Status	Name	Step	Test failures	Logs	Raw logs
✔️	JVM Tests - JDK 11
✖	JVM Tests - JDK 11 Windows	Build	⚠️ Check →	Logs	Raw logs
✖	JVM Tests - JDK 16	Build	Test failures	Logs	Raw logs

Full information is available in the Build summary check run.

Test Failures

⚙️ JVM Tests - JDK 16 #

📦 extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment

✖ io.quarkus.resteasy.reactive.server.test.simple.SimpleQuarkusRestTestCase.testException line 165 - More details - Source on GitHub

java.lang.AssertionError: 
1 expectation failed.
Response body doesn't match expectation.
Expected: "OK"
  Actual: An Internal Server Error with stack trace:
java.lang.NullPointerException: Cannot invoke "org.jboss.resteasy.reactive.server.core.ResteasyReactiveRequestContext.getTarget()" because the return value of "org.jboss.resteasy.reactive.server.injection.ContextProducers.getContext()" is null
	at org.jboss.resteasy.reactive.server.injection.ContextProducers.getTarget(ContextProducers.java:108)
	at org.jboss.resteasy.reactive.server.injection.ContextProducers.resourceInfo(ContextProducers.java:90)
	at org.jboss.resteasy.reactive.server.injection.ContextProducers_ProducerMethod_resourceInfo_be7f5503a87442251cde9fbc1d406fb350a529f0_Bean.create(ContextProducers_ProducerMethod_resourceInfo_be7f5503a87442251cde9fbc1d406fb350a529f0_Bean.zig:163)
	at org.jboss.resteasy.reactive.server.injection.ContextProducers_ProducerMethod_resourceInfo_be7f5503a87442251cde9fbc1d406fb350a529f0_Bean....