[RELEASE] Prepare release 1.16.0

[marcalff]

No date yet.

Tentative content:

• [SEMANTIC CONVENTIONS] Upgrade to version 1.26.0 #2687
• [bazel] Bump version and deps #2679
• [BUILD] Restore Bazel flag removed from public API #2702
• [EXPORTER] OTLP file: use thread-safe file/io #2675
• [API/SDK] Provider cleanup #2664
• [BUILD] Add support for bzlmod #2608
• [Code health] include-what-you-use cleanup #2054
  • [Code health] include-what-you-use cleanup #2692

Postponed:

• messaging.client_id -> messaging.client.id rename causes issues with code generation semantic-conventions#1031
  • Need a new release of build-tools, to resolve semconv name collisions
  • Remove the hard coded logic for messaging.client_id
• [feature] Build tools/schema should define code-friendly attribute/metric/event/etc names build-tools#323