crypto: Vendor openssl package

[qmuntal]

Important:

• This PR will be rebased to microsoft/dev.boringcrypto.go1.17 once crypto: Use openssl instead of boring #364.
• github.com/microsoft/go-crypto-openssl will point to main instead of dev/qmuntal/openssl once Port openssl package go-crypto-openssl#1 is merged.

This PR remove the crypto/internal/backend/internal/openssl package in favor of the external package github.com/microsoft/go-crypto-openssl, which is copied into the source tree as a vendored package.

The vendoring process is explained in https://github.com/golang/go/blob/master/src/README.vendor.

The commands I used to vendor openssl are the following:

// The next line can be skipped once the openssl repo is made public.
go env -w GOPRIVATE=github.com/microsoft/*

go get -d github.com/microsoft/go-crypto-openssl@dev/qmuntal/openssl
go mod tidy
go mod vendor