Support Spring Boot 4 auto configuration

[typefield]

What is the purpose of the change

Support Spring Boot 4 for Dubbo Spring Boot integration.

Fixes #16214.

Brief changelog

• Add dubbo-spring-boot-4-autoconfigure and dubbo-spring-boot-starter4 modules.
• Add Spring Boot 4 Triple servlet/websocket auto-configuration using the Spring Boot 4 Tomcat factory API.
• Keep Spring Boot 3 auto-configuration scoped to Boot 3 and add a dedicated Boot 4 dependency check auto-configuration.
• Add Boot 4 auto-configuration smoke tests for Triple servlet, websocket, defaults, and Tomcat HTTP/2 customization.

Verifying this change

• ./mvnw -pl dubbo-spring-boot-project/dubbo-spring-boot-4-autoconfigure -am -P spring-boot-4 -Dtest=DubboTriple4AutoConfigurationTest -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false -Dspotless.check.skip=true -Dlicense.skip=true -Dcheckstyle.skip=true test
• ./mvnw -pl dubbo-spring-boot-project/dubbo-spring-boot-autoconfigure,dubbo-spring-boot-project/dubbo-spring-boot-4-autoconfigure,dubbo-spring-boot-project/dubbo-spring-boot-starters/dubbo-spring-boot-starter4 -am -P spring-boot-4 -DskipTests -Dspotless.check.skip=true -Dlicense.skip=true compile
• ./mvnw -pl dubbo-spring-boot-project/dubbo-spring-boot-autoconfigure,dubbo-spring-boot-project/dubbo-spring-boot-3-autoconfigure,dubbo-spring-boot-project/dubbo-spring-boot-4-autoconfigure -P spring-boot-4 -DskipTests spotless:check

Note: a broader -am test run was stopped by pre-existing or environment-sensitive failures in dubbo-common before reaching this module, so the verification above narrows the test run to the new Boot 4 test while compiling the required reactor.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 48.33333% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.83%. Comparing base (2626e28) to head (61235c2).
⚠️ Report is 1 commits behind head on 3.3.

Files with missing lines	Patch %	Lines
...t/autoconfigure/DubboTriple4AutoConfiguration.java	66.66%	8 Missing ⚠️
...pring/boot/autoconfigure/SpringBoot4Condition.java	45.45%	3 Missing and 3 partials ⚠️
...pring/boot/autoconfigure/SpringBoot3Condition.java	33.33%	3 Missing and 3 partials ⚠️
...oot/autoconfigure/SpringBoot4OrLaterCondition.java	45.45%	3 Missing and 3 partials ⚠️
...boSpringBoot4DependencyCheckAutoConfiguration.java	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #16360      +/-   ##
============================================
+ Coverage     60.81%   60.83%   +0.02%     
- Complexity       30    11763   +11733     
============================================
  Files          1953     1957       +4     
  Lines         89213    89272      +59     
  Branches      13460    13468       +8     
============================================
+ Hits          54254    54309      +55     
- Misses        29374    29378       +4     
  Partials       5585     5585              

Flag	Coverage Δ
integration-tests-java21	32.08% <0.00%> (-0.08%)	⬇️
integration-tests-java8	32.21% <0.00%> (+0.02%)	⬆️
samples-tests-java21	32.20% <9.80%> (+0.04%)	⬆️
samples-tests-java8	29.82% <9.80%> (+<0.01%)	⬆️
unit-tests-java11	59.07% <32.00%> (+0.01%)	⬆️
unit-tests-java17	58.57% <48.33%> (+0.01%)	⬆️
unit-tests-java21	58.57% <48.33%> (+0.02%)	⬆️
unit-tests-java25	58.50% <48.33%> (+<0.01%)	⬆️
unit-tests-java8	59.08% <32.00%> (-0.04%)	⬇️

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