Add support for POINT_CONVERSION_HYBRID (#1936)

This is the first time it has come up, but Ruby depends on the
`POINT_CONVERSION_HYBRID` format in its tests and expects the underlying
libcrypto to support it. There's not too much a difference between
`POINT_CONVERSION_HYBRID` and
`POINT_CONVERSION_UNCOMPRESSED` except that the first bit contains
information about the quadratic equation y is at. We have the building
blocks to support and can get this working with some tweaking around.
Most of this change is working with the first byte
`POINT_CONVERSION_HYBRID` does differently and point the encoding to
the right places for parsing.

### Testing:
* Testing parsing from and back with `POINT_CONVERSION_HYBRID`. What
we're parsing to and from hybrid doesn't really matter here, they're
already covered by other code paths.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license and the ISC license.

crypto/fipsmodule/ec/ec.c

@@ -1152,12 +1152,6 @@ int EC_METHOD_get_field_type(const EC_METHOD *meth) {
 
 void EC_GROUP_set_point_conversion_form(EC_GROUP *group,
                                         point_conversion_form_t form) {
-  /* NO-OP. However, abort if consumer attempts to set a representation that is
-   * not supported. */
-  if (form != POINT_CONVERSION_UNCOMPRESSED &&
-      form != POINT_CONVERSION_COMPRESSED) {
-    abort();
-  }
   // |conv_form| can only be set with OpenSSL compatible dynamically allocated
   // groups.
   if (group->mutable_ec_group) {