Unwind M_ASN1_* macros for primitive types.

At one point in the SSLeay days, all the ASN1_STRING typedefs were
separate structs (but only in debug builds) and the M_ASN1_* macros
included type casts to handle this.

This is long gone, but we still have the M_ASN1_* macros. Remove the
casts and switch code within the library to call the macros. Some

- The "MSTRING" types (what OpenSSL calls its built-in CHOICEs
  containing some set of string types) are weird because the M_FOO_new()
  macro and the tasn_new.c FOO_new() function behave differently. I've
  split those into a separate CL.

- ASN1_STRING_type, etc., call into the macro, which accesses the field
  directly. This CL inverts the dependency.

- ASN1_INTEGER_new and ASN1_INTEGER_free, etc., are generated via
  IMPLEMENT_ASN1_STRING_FUNCTIONS in tasn_typ.c. I've pointed
  M_ASN1_INTEGER_new and M_ASN1_INTEGER_free to these fields. (The free
  function is a no-op, but consistent.)

- The other macros like M_ASN1_BIT_STRING_dup largely do not have
  corresponding functions. I've aligned with OpenSSL in just using the
  generic ASN1_STRING_dup function. But some others, like
  M_ASN1_OCTET_STRING_dup have a corresponding ASN1_OCTET_STRING_dup
  function. OpenSSL retained these, so I have too.

Update-Note: Some external code uses the M_ASN1_* macros. This should
remain compatible, but some type errors may have gotten through
unnoticed. This CL restores type-checking.

Change-Id: I8656abc7d0f179192e05a852c97483c021ad9b20
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/44045
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/asn1/a_utctm.c b/crypto/asn1/a_utctm.c
index f7519df..d5bd0e4 100644
--- a/crypto/asn1/a_utctm.c
+++ b/crypto/asn1/a_utctm.c
@@ -197,7 +197,7 @@
     if (s == NULL) {
         free_s = 1;
-        s = M_ASN1_UTCTIME_new();
+        s = ASN1_UTCTIME_new();
     if (s == NULL)
         goto err;
@@ -234,7 +234,7 @@
     return (s);
     if (free_s && s)
-        M_ASN1_UTCTIME_free(s);
+        ASN1_UTCTIME_free(s);
     return NULL;