Fix --annotated + --size-prefixed generating empty annotated files

[dataCenter430]

Closes: #8953

Summary

• Fixes an issue where running flatc --size-prefixed --annotated <schema>.fbs -- <binary> would generate an almost empty annotated file.
• Ensures that the reflection schema used by BinaryAnnotator is always validated as a normal (non–size-prefixed) schema, independent of whether the input binary is size-prefixed.
• Keeps is_size_prefixed_ scoped correctly to parsing the data buffer header only.

Description

Previously, BinaryAnnotator::Annotate validated the schema buffer like this:

• If is_size_prefixed_ was true (because the input binary was size-prefixed), it attempted reflection::VerifySizePrefixedSchemaBuffer.
• If that failed, or if reflection::VerifySchemaBuffer failed, it returned an empty section map.

In the --annotated flow, the schema (.bfbs) is not size-prefixed, even when the binary data is. This caused schema verification to fail when --size-prefixed was used, leading to an empty annotation result and an almost empty .afb file.

This PR changes BinaryAnnotator::Annotate to always validate the schema using:

if (!reflection::VerifySchemaBuffer(verifier)) {
  return {};
}

[dataCenter430]

Hi, @dbaileychess
Please reivew the PR when you have a chance.
Thanks