refactor(builtin): merge pair.lean with kernel.lean, and add basic theorems

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/elaborator): fix glitches in the elaborator that were forcing us to provide parameters explicitly

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/elaborator): fix glitches in the elaborator that were forcing us to provide parameters explicitly