[llvm][NFC] Move content of ML subdirectory into Analysis

The initial intent was to organize ML stuff in its own directory, but
it turns out that conflicts with llvm component layering policies: it
is not a component, because subsequent changes want to rely on other
analyses, which would create a cycle; and we don't have a reliable,
cross-platform mechanism to compile files in a subdirectory, and fit in
the existing LLVM build structure.

This change moves the files into Analysis, and subsequent changes will
leverage conditional compilation for those that have optional
dependencies.