RFR: 8370800: Downgrade cant.attach.type.annotations diagnostics to warnings

[Liam Miller-Cushon]

Hi, please consider this fix for [JDK-8370800: Downgrade cant.attach.type.annotations diagnostics to warnings](https://bugs.openjdk.org/browse/JDK-8370800).

As discussed in the, this reduces the compatibility impact of these diagnostics for builds that deliberately omit transitive annotation dependencies, for example if they are only referenced through javadoc `@link` tags, or by frameworks that conditionally load the classes.

The PR changes the existing error diagnostic to an unconditional warning. Another alternative would be to make it an optional xlint diagnostic, perhaps as part of `-Xlint:classfile`, or as another category.

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Commit messages:
 - 8370800: Downgrade cant.attach.type.annotations diagnostics to warnings

Changes: https://git.openjdk.org/jdk/pull/28018/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28018&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370800
  Stats: 11 lines in 3 files changed: 3 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/28018.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28018/head:pull/28018

PR: https://git.openjdk.org/jdk/pull/28018