Generate opt-in instrumentation version class

[trask]

Alternative to #18600

Primarily motivated by putting the InstrumentationVersion class into the instrumentation's "correct" package (semi-related to #18428).

cc @breedx-splk @LikeTheSalad

[Copilot]

Pull request overview

This PR introduces an opt-in mechanism for instrumentation libraries to supply their instrumentation version via a generated Java class (instead of always reading META-INF/...properties at runtime), and updates InstrumenterBuilder to only fall back to embedded properties when a version wasn’t explicitly provided. This supports Android-sensitive environments by avoiding resource reads when instrumentations opt in.

Changes:

• Add a new Gradle convention plugin (otel.instrumentation-version-class) that generates a configurable InstrumentationVersion Java class containing a VERSION constant.
• Make InstrumenterBuilder lazily resolve the embedded instrumentation version only at build time, and only if no explicit version was set.
• Opt okhttp-3.0 library instrumentation into the generated version class and set the instrumenter version via builder customization.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
instrumentation/okhttp/okhttp-3.0/library/src/main/java/io/opentelemetry/instrumentation/okhttp/v3_0/internal/OkHttpClientInstrumenterBuilderFactory.java	Sets the instrumentation version explicitly using the generated InstrumentationVersion.VERSION.
instrumentation/okhttp/okhttp-3.0/library/build.gradle.kts	Applies the new generator plugin and configures the generated class’ fully qualified name.
instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/InstrumenterBuilder.java	Defers embedded version lookup until instrumenter build time and only when needed.
conventions/src/main/kotlin/otel.instrumentation-version-class.gradle.kts	New convention plugin wiring generation into the main source set and build tasks.
conventions/src/main/kotlin/io/opentelemetry/instrumentation/gradle/InstrumentationVersionClassExtension.kt	Adds a Gradle extension to configure the generated class name.
conventions/src/main/kotlin/io/opentelemetry/instrumentation/gradle/GenerateInstrumentationVersionClassTask.kt	Implements the task that generates the Java source containing the VERSION constant.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

[laurit]

I think I like this more since we need to add the version file only for instrumentations that android uses and I guess they don't care about other instrumentations besides okhttp.