[lldb] Provide GetHomeDirectory wrapper in Host::FileSystem (NFC)

[Teemperor]

Provider a wrapper around llvm::sys::path::home_directory in the
FileSystem class. This will make it possible for the reproducers to
intercept the call in a central place.

(cherry picked from commit 921c1b7)

Backported as a 040f52c (which was backported) calls this function and otherwise the branch doesn't compile.

[Teemperor]

@swift-ci smoke test

[Teemperor]

Branch is currently failing with

11:30:43  /var/lib/jenkins/workspace/apple-stable/llvm-project/lldb/source/Interpreter/CommandInterpreter.cpp:2102:26: error: no member named 'GetHomeDirectory' in 'lldb_private::FileSystem'
11:30:43    FileSystem::Instance().GetHomeDirectory(init_file);
11:30:43    ~~~~~~~~~~~~~~~~~~~~~~ ^
11:30:43  1 error generated.

[Teemperor]

@swift-ci test

[JDevlieghere]

Thanks!