Fixed accidental use of String.isEmpty in SimpleCommandLineArgsParser

Issue: SPR-11321
Polishing
Introduced customizeConnection callbacks for URLConnection used by exists() / contentLength() / lastModified()

Issue: SPR-11320
(cherry picked from commit 4f45ad5)
Polishing
Fixed assert in setAspectJAdvisorFactory()

Issue: SPR-11330
(cherry picked from commit f15a5fe)
Added info-level logging for default unit detection

Issue: SPR-11333
(cherry picked from commit 88730bd)
Consistent evaluation of empty theme names to default theme name

Issue: SPR-11128
(cherry picked from commit cc81aae)
Locale/ThemeChangeInterceptor alignment and javadoc polishing

Issue: SPR-11128
(cherry picked from commit 5e5add4)
Polishing
Ensure all tests in spring-test are executed

Prior to this commit TestNG tests would only be executed by the Gradle
build if they were located in the “testng” package. Tests in subpackages
would therefore be omitted from the build.

This commit ensures that all TestNG classes in the “testng” package and
any of its subpackages are executed in the Gradle build.

Furthermore, this commit ensures that the JUnit-based
FailingBeforeAndAfterMethodsTests test class is executed along with the
other JUnit tests even though it resides under the “testng” package.

Issue: SPR-11338

Backport-Commit: 098d7c746532135e0edc241d91dfc1f27389949d
Include ServletTEL in abstract base test classes

The ServletTestExecutionListener is now prepended to the set of default
listeners in AbstractJUnit4SpringContextTests and
AbstractTestNGSpringContextTests.

Issue: SPR-11340

Backport-Commit: 3370f8b1b10ccdcd9c29e6d36560c07191112c31
Removed accidental backport of StAX code in 3.2.5 (restoring Java 5 compatibility)

Issue: SPR-11341
Fixed setDeliveryPersistent javadoc

Issue: SPR-3983
(cherry picked from commit 9cc86a3)