[Coroutines][1/6] New pass manager: coro-early

Summary:
The first in a series of patches that ports the LLVM coroutines passes
to the new pass manager infrastructure. This patch implements
'coro-early'.

NB: All coroutines passes begin by checking that coroutine intrinsics are
declared within the LLVM IR module they're operating on. To do so, they call
`coro::declaresIntrinsics`. The next 3 patches in this series, which add new
pass manager implementations of the 'coro-split', 'coro-elide', and
'coro-cleanup' passes, use a similar pattern as the one used here: a static
function is shared across both old and new passes to detect if relevant
coroutine intrinsics are delcared. To make this pattern easier to read, this
patch adds `const` keywords to the parameters of `coro::declaresIntrinsics`.

Reviewers: GorNishanov, lewissbaker, junparser, chandlerc, deadalnix, wenlei

Reviewed By: wenlei

Subscribers: ychen, wenlei, EricWF, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71898