Add value() and name() methods to enum types.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/Kms/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:854131ec1af7b3a313253474c24748dc0acd217a58a0b74dbfb559f340a15d78
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/kms/artman_cloudkms.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-kms-v1.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/KeyManagementServiceClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/KeyManagementServiceGrpcClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/Gapic/KeyManagementServiceGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/KeyManagementServiceClientTest.php.
synthtool > Replaced 'CryptoKey_CryptoKeyPurpose' in src/V1/Gapic/KeyManagementServiceGapicClient.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKeyVersion_CryptoKeyVersionView.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKeyVersion_CryptoKeyVersionAlgorithm.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKey_CryptoKeyPurpose.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKeyVersion_CryptoKeyVersionState.php.
synthtool > Cleaned up 1 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[codecov]

Codecov Report

Merging #1777 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1777   +/-   ##
=========================================
  Coverage     91.53%   91.53%           
  Complexity     4360     4360           
=========================================
  Files           304      304           
  Lines         12901    12901           
=========================================
  Hits          11809    11809           
  Misses         1092     1092

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