[BUG] another peerOptional ERESOLVE case

[isaacs]

Missed a case in #223

root -> (x, z@1)
x -> PEEROPTIONAL(y)
y -> PEER(z@2)

This is subtly similar to case A

case A, hidden to not be confusing

# case a
root -> (x, y@1)
x -> PEEROPTIONAL(z)
z -> PEER(y@2)

But, with the names spelled in such a way that the conflicted dep is not present in the peerSet tree until after the not-required peerOptional meta-peer is added. (They are sorted alphabetically for consistency.)

This code path wasn't being hit previously, and it's what prevents ng-packagr@11.1.3 from being installed alongside typescript@4. Ie,

x = ng-packagr@11.1.3
y = tsickle
z@1 = typescript@4
z@2 = typescript@~3.9.5

What / Why

n/a

When

• n/a

Where

• n/a

How

Current Behavior

• n/a

Steps to Reproduce

• n/a

Expected Behavior

• n/a

Who

• n/a

References

• n/a

[isaacs]

Ok, took a bit more work to get a reproduction case that actually is broken in the same way. Got to it with this:

root -> (x, z@1)
x -> PEEROPTIONAL(y) PEER(z@1) PEER(w@1)
w -> PEER(z@1)
y -> PEER(z@2)

PR incoming.