RFR: 8366483: ShowRegistersOnAssertTest uses wrong register pattern string for Windows on AArch64

[Saint Wesonga]

ShowRegistersOnAssertTest.java verifies that registers are printed in the error log when VMError::controlled_crash() is called. However, it searches for the pattern "R0=", which is valid on Linux AArch64 only. The Windows AArch64 [os::print_context](https://github.com/openjdk/jdk/blob/999761d0f6d37c9cd6ec482620800b694c5fb9ad/src/hotspot/os_cpu/windows_aarch64/os_windows_aarch64.cpp#L184-L186) implementation outputs registers in the format "X0 =". This change updates the test to use this pattern on the Windows AArch64 platform. The test passes with this change.

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Commit messages:
 - Fix register matching string on Windows

Changes: https://git.openjdk.org/jdk/pull/27022/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27022&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366483
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27022.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27022/head:pull/27022

PR: https://git.openjdk.org/jdk/pull/27022