[bazel_migration] Migrate diagnostics log libraries

Migrate Rust diagnostics logging libraries to Bazel and let bazel2gn
generate their GN equivalents:

  //src/lib/diagnostics/log/encoding/rust
  //src/lib/diagnostics/log/rust

Note: test_deps intentionally name targets that are not migrated yet,
so the generated Bazel *_test targets do not analyze. They are
declared now to keep bazel2gn's GN output in sync; the GN tests are
unaffected.

Test: fx bazel build --config=fuchsia_platform \
    //src/lib/diagnostics/log/encoding/rust \
    //src/lib/diagnostics/log/rust \
    //src/lib/diagnostics/log/rust:no_startup_handle
Test: fx build --host \
    @//src/lib/diagnostics/log/encoding/rust \
    @//src/lib/diagnostics/log/rust
Test: fx build --host //build:bazel2gn_verifications
Test: fx build

Change-Id: I7782d6885201d904caa8f8f0b42eb1666a6a6964
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1834289
Reviewed-by: Wayne Chou <waynechou@google.com>
Commit-Queue: Jay Zhuang <jayzhuang@google.com>
Presubmit-Verified: fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com <fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com>