Align EVP_PKEY Ed25519 API with upstream.

Rather than adding a new mode to EVP_PKEY_CTX, upstream chose to tie
single-shot signing to EVP_MD_CTX, adding functions which combine
EVP_Digest*Update and EVP_Digest*Final. This adds a weird vestigial
EVP_MD_CTX and makes the signing digest parameter non-uniform, slightly
complicating things. But it means APIs like X509_sign_ctx can work
without modification.

Align with upstream's APIs. This required a bit of fiddling around
evp_test.cc. For consistency and to avoid baking details of parameter
input order, I made it eagerly read all inputs before calling
SetupContext. Otherwise which attributes are present depend a lot on the
shape of the API we use---notably the NO_DEFAULT_DIGEST tests for RSA
switch to failing before consuming an input, which is odd.

(This only matters because we have some tests which expect the operation
to abort the operation early with parameter errors and match against
Error. Those probably should not use FileTest to begin with, but I'll
tease that apart a later time.)

Upstream also named NID_Ed25519 as NID_ED25519, even though the
algorithm is normally stylized as "Ed25519". Switch it to match.

Change-Id: Id6c8f5715930038e754de50338924d044e908045
Reviewed-on: https://boringssl-review.googlesource.com/17044
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/crypto/obj/obj_mac.num b/crypto/obj/obj_mac.num
index 2f2a557..572a01b 100644
--- a/crypto/obj/obj_mac.num
+++ b/crypto/obj/obj_mac.num
@@ -937,4 +937,4 @@
 dh_std_kdf		946
 dh_cofactor_kdf		947
 X25519		948
-Ed25519		949
+ED25519		949