feat(frontends/lean/inductive_cmd): prefix introduction rules with the name of the inductive datatype

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library): add 'and' namespace

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library): add 'eq' and 'ne' namespaces

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>