RFR: 8344259: Annotate Float16 with jdk.internal.ValueBased

[Paul Sandoz]

Annotate `Float16` with `jdk.internal.ValueBased`. This requires we export the package `jdk.internal` in module `java.base` to module` jdk.incubator.vector`.

Doing so enables the compiler and runtime to report warnings about improper attempts to synchronize on instances of `Float16`, as described in [JEP 390](https://openjdk.org/jeps/390).

-------------

Commit messages:
 - 8344259: Annotate Float16 with jdk.internal.ValueBased

Changes: https://git.openjdk.org/jdk/pull/22128/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22128&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344259
  Stats: 5 lines in 2 files changed: 2 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22128.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22128/head:pull/22128

PR: https://git.openjdk.org/jdk/pull/22128