Add missing `OpenSSL::PKey::EC#to_text` method

[postmodern]

I noticed that on JRuby 9.4.3.0 that the OpenSSL::PKey::EC#to_text method is missing.

Steps To Reproduce

ec = OpenSSL::PKey::EC.new(File.read('ec.pem'))
# => #<OpenSSL::PKey::EC:0x2786b644>
puts ec.to_text

Expected Result

Private-Key: (256 bit)
priv:
    28:a1:46:a1:c5:08:09:5c:c4:4b:49:6c:fb:7c:9d:
    71:3a:31:40:f2:03:b8:1a:0f:e0:44:e1:51:74:b3:
    9f:3a
pub:
    04:04:4b:ce:10:9e:ef:33:eb:5e:35:f6:cc:a4:97:
    95:f5:28:3d:e9:1e:9a:67:aa:0e:f8:ea:25:e0:3d:
    7c:00:fa:46:27:72:b4:3e:bd:18:4a:39:8d:32:ae:
    ce:63:76:d6:dc:cc:5a:91:d9:a7:a2:af:cc:49:99:
    4a:d0:d6:3e:53
ASN1 OID: prime256v1
NIST CURVE: P-256

Actual Result

(irb):2:in `evaluate': undefined method `to_text' for #<OpenSSL::PKey::EC:0x2786b644> (NoMethodError)
	from org/jruby/RubyKernel.java:1159:in `eval'
	from org/jruby/RubyKernel.java:1601:in `loop'
	from org/jruby/RubyKernel.java:1308:in `catch'
	from org/jruby/RubyKernel.java:1308:in `catch'
	from /opt/rubies/jruby-9.4.3.0/lib/ruby/gems/shared/gems/irb-1.4.2/exe/irb:11:in `<main>'
	from org/jruby/RubyKernel.java:1105:in `load'
	from /opt/rubies/jruby-9.4.3.0/bin/irb:23:in `<main>'