Rename servlet common snippet package

[trask]

Part of

• Tracking package and module name alignment #18428

[Copilot]

Pull request overview

Pure package rename: moves the two snippet helper classes from io.opentelemetry.javaagent.instrumentation.servlet.snippet to io.opentelemetry.javaagent.instrumentation.servlet.common.snippet to align with the directory layout under servlet-common, and updates all importers in servlet-3.0 and servlet-5.0.

Changes:

• Update package declaration on SnippetInjectingPrintWriter and OutputStreamSnippetInjectionHelper.
• Update imports in servlet-3.0/5.0 wrappers, singletons, and unit tests.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
servlet-common/.../snippet/SnippetInjectingPrintWriter.java	Package declaration moved under .common.snippet.
servlet-common/.../snippet/OutputStreamSnippetInjectionHelper.java	Package declaration moved under .common.snippet.
servlet-5.0/.../Servlet5SnippetInjectingResponseWrapper.java	Import updated to new package.
servlet-5.0/.../Servlet5Singletons.java	Import updated to new package.
servlet-5.0 javaagent-unit-tests/.../SnippetServletOutputStreamTest.java	Import updated to new package.
servlet-3.0/.../Servlet3SnippetInjectingResponseWrapper.java	Import updated to new package.
servlet-3.0/.../Servlet3Singletons.java	Import updated to new package.
servlet-3.0 javaagent-unit-tests/.../SnippetServletOutputStreamTest.java	Import updated to new package.