move declarative config ObjectMapper instance to internal class

[zeitlinger]

Is your feature request related to a problem? Please describe.

Spring starter with declarative config needs to use the same settings for object mapper as

opentelemetry-java/sdk-extensions/incubator/src/main/java/io/opentelemetry/sdk/extension/incubator/fileconfig/DeclarativeConfiguration.java

Line 66 in e658462

static final ObjectMapper MAPPER;

See open-telemetry/opentelemetry-java-instrumentation#14062 (comment)

Describe the solution you'd like

Move the instance to an internal class where it can be read without reflection.

Describe alternatives you've considered

Read the instance using reflection.

[trask]

any other options? it would be nice not to introduce new reliance on internals where possible (#6970)

[zeitlinger]

any other options? it would be nice not to introduce new reliance on internals where possible (#6970)

This is what I can think of - there really is a strong reliance on the jackson settings after all:

• copy-paste (what we have now)
• reflection
• internal class

[trask]

I personally prefer a bit of copy-paste over relying on internal APIs