[jdk18] RFR: 8272058: 25 Null pointer dereference defect groups in 4 files

[Daniel D.Daugherty]

A small refactoring to resolve a Parfait complaint about the return value from
`MacroAssembler::target_addr_for_insn(address insn_addr, unsigned insn)`
on AARCH64. The logic that supports returning `nullptr` as the target addr for
a particular instruction is moved from
`MacroAssembler::target_addr_for_insn(address insn_addr, unsigned insn)` to
`MacroAssembler::target_addr_for_insn_allow_null_ret(address insn_addr, unsigned insn)`.
A couple of `target_addr_for_insn()` call sites that can tolerate a `nullptr` are
converted to use `target_addr_for_insn_allow_null_ret()`.

This fix has been tested with Mach5 Tier[1-3].

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Commit messages:
 - 8272058.exp1.patch

Changes: https://git.openjdk.java.net/jdk18/pull/51/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=51&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272058
  Stats: 18 lines in 3 files changed: 13 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/51.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/51/head:pull/51

PR: https://git.openjdk.java.net/jdk18/pull/51