RFR: 8373046: Method::get_c2i_unverified_entry() and get_c2i_no_clinit_check_entry() are missing check for abstract method

[Ashutosh Mehra]

This PR fixes a bug introduced by [JDK-8365501](https://bugs.openjdk.org/browse/JDK-8365501). It restores the behavior of `Method::get_c2i_unverified_entry` or `Method::get_c2i_no_clinit_check_entry` for abstract methods as it was before JDK-8365501. It was never the intention of JDK-8365501 to change the behavior.
I am not sure if there is any possible code flow that can result in calling `Method::get_c2i_unverified_entry` or `Method::get_c2i_no_clinit_check_entry` for abstract methods, but I think it is safe to keep the behavior of these functions as before.

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Commit messages:
 - 8373046: Method::get_c2i_unverified_entry() and get_c2i_no_clinit_check_entry() are missing check for abstract method

Changes: https://git.openjdk.org/jdk/pull/28645/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28645&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373046
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28645.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28645/head:pull/28645

PR: https://git.openjdk.org/jdk/pull/28645