RFR: 8331027: JDK's ct.sym file packs corrupted module-info classes

[Jan Lahoda]

When writing the `ModuleMainClass` attribute, `CreateSymbols` uses an UTF8 entry (incorrect), instead of a Class_info (correct). This patch fixes that.

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Commit messages:
 - 8331027: JDK's ct.sym file packs corrupted module-info classes

Changes: https://git.openjdk.org/jdk/pull/19031/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19031&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331027
  Stats: 240 lines in 4 files changed: 208 ins; 10 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/19031.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19031/head:pull/19031

PR: https://git.openjdk.org/jdk/pull/19031