[lldb][FreeBSDKernel] Find .debug files using pseudo sysroot (#224845)

Unlike userspace processes, it is common to obtain kernel dump from a
machine (e.g. QEMU) which different from the machine debugging the dump.
In this case users need to run `target symbols add foo.debug` for the
kernel and each kernel object, which becomes quite inconvenient when the
machine had dozens of kernel modules loaded during the dump.

This patch adds functionality to the dynamic loader so that it loads
symbol files automatically when kernel or kenrel modules are loaded. It
assumes a pseudo sysroot. When kernel is located at
`/foo/boot/kernel/kernel`, it will look for
`foo/usr/lib/debug/boot/kernel/kernel.debug` and same for kernel
modules. In this case, the only thing users need to do is copying the
dumped machine's `/usr/lib/debug/boot` relative to `/boot` that is being
debugged.

Assisted-by: GPT
GitOrigin-RevId: 2590e4e2d10606000821336f3a163a0ac6b4d77d