docs: Update documentation and tests.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/Language/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:846102ebf7ea2239162deea69f64940443b4147f7c2e68d64b332416f74211ba
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/language/artman_language_v1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-language-v1.
synthtool > Running generator for google/cloud/language/artman_language_v1beta2.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-language-v1beta2.
synthtool > Replaced 'Copyright \\d{4}' in src/V1beta2/LanguageServiceClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1beta2/LanguageServiceGrpcClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1beta2/Gapic/LanguageServiceGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/System/V1beta2/LanguageServiceSmokeTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1beta2/LanguageServiceClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/LanguageServiceClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/LanguageServiceGrpcClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/Gapic/LanguageServiceGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/System/V1/LanguageServiceSmokeTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/LanguageServiceClientTest.php.
synthtool > No replacements made in src/*/Gapic/LanguageServiceGapicClient.php for pattern AnnotateTextRequest_Features, maybe replacement is not longer needed?
synthtool > Cleaned up 0 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d5fa88e). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2006   +/-   ##
=========================================
  Coverage          ?   92.56%           
  Complexity        ?     4374           
=========================================
  Files             ?      303           
  Lines             ?    12996           
  Branches          ?        0           
=========================================
  Hits              ?    12030           
  Misses            ?      966           
  Partials          ?        0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d5fa88e...63d1169. Read the comment docs.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d5fa88e). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2006   +/-   ##
=========================================
  Coverage          ?   92.56%           
  Complexity        ?     4374           
=========================================
  Files             ?      303           
  Lines             ?    12996           
  Branches          ?        0           
=========================================
  Hits              ?    12030           
  Misses            ?      966           
  Partials          ?        0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d5fa88e...63d1169. Read the comment docs.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d5fa88e). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2006   +/-   ##
=========================================
  Coverage          ?   92.57%           
  Complexity        ?     4378           
=========================================
  Files             ?      304           
  Lines             ?    13012           
  Branches          ?        0           
=========================================
  Hits              ?    12046           
  Misses            ?      966           
  Partials          ?        0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d5fa88e...cb6ebf5. Read the comment docs.

[googlebot]

So there's good news and bad news.

👍 The good news is that everyone that needs to sign a CLA (the pull request submitter and all commit authors) have done so. Everything is all good there.

😕 The bad news is that it appears that one or more commits were authored or co-authored by someone other than the pull request submitter. We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that here in the pull request.

Note to project maintainer: This is a terminal state, meaning the cla/google commit status will not change from this state. It's up to you to confirm consent of all the commit author(s), set the cla label to yes (if enabled on your project), and then merge this pull request when appropriate.

ℹ️ Googlers: Go here for more info.

[googlebot]

A Googler has manually verified that the CLAs look good.

(Googler, please make sure the reason for overriding the CLA status is clearly documented in these comments.)

ℹ️ Googlers: Go here for more info.