[lldb][test] Support remote run of Shell tests (#95986)
1. This commit adds LLDB_TEST_PLATFORM_URL, LLDB_TEST_SYSROOT,
LLDB_TEST_PLATFORM_WORKING_DIR, LLDB_SHELL_TESTS_DISABLE_REMOTE cmake
flags to pass arguments for cross-compilation and remote running of both Shell&API tests.
2. To run Shell tests remotely, it adds 'platform select' and 'platform connect' commands to %lldb
substitution.
3. 'remote-linux' feature added to lit to disable tests failing with
remote execution.
4. A separate working directory is assigned to each test to avoid
conflicts during parallel test execution.
5. Remote Shell testing is run only when LLDB_TEST_SYSROOT is set for
building test sources. The recommended compiler for that is Clang.
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Co-authored-by: Vladimir Vereschaka <vvereschaka@accesssoftek.com>
