[lldb][Process/FreeBSDKernelCore] Implement DoWriteMemory() (#183553)
Implement `ProcessFreeBSDKernelCore::DoWriteMemory()` to write data on
kernel crash dump or `/dev/mem`. Due to safety reasons (e.g. writing
wrong value on `/dev/mem` can trigger kernel panic), this feature is
only enabled when `plugin.process.freebsd-kernel-core.read-only` is set
to false (true by default).
Since 85a1fe6 (#183237) was reverted as it was prematurely merged, I'm
committing changes again with corrections here.
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Signed-off-by: Minsoo Choo <minsoochoo0122@proton.me>