[SPARK-29569][BUILD][DOCS] Copy and paste minified jquery instead when post-processing badges in JavaDoc

[HyukjinKwon]

What changes were proposed in this pull request?

This PR fixes our documentation build to copy minified jquery file instead.

The original file jquery.js seems missing as of Scala 2.12 upgrade. Scala 2.12 seems started to use minified jquery.min.js instead.

Since we dropped Scala 2.11, we won't have to take care about legacy jquery.js anymore.

Note that, there seem multiple weird stuff in the current ScalaDoc (e.g., some pages are weird, it starts from scala.collection.* or some pages are missing, or some docs are truncated, some badges look missing). It needs a separate double check and investigation.

This PR targets to make the documentation generation pass in order to unblock Spark 3.0 preview.

Why are the changes needed?

To fix and make our official documentation build able to run.

Does this PR introduce any user-facing change?

It will enable to build the documentation in our official way.

Before:

Making directory api/scala
cp -r ../target/scala-2.12/unidoc/. api/scala
Making directory api/java
cp -r ../target/javaunidoc/. api/java
Updating JavaDoc files for badge post-processing
Copying jquery.js from Scala API to Java API for page post-processing of badges
jekyll 3.8.6 | Error:  No such file or directory @ rb_sysopen - ./api/scala/lib/jquery.js

After:

Making directory api/scala
cp -r ../target/scala-2.12/unidoc/. api/scala
Making directory api/java
cp -r ../target/javaunidoc/. api/java
Updating JavaDoc files for badge post-processing
Copying jquery.min.js from Scala API to Java API for page post-processing of badges
Copying api_javadocs.js to Java API for page post-processing of badges
Appending content of api-javadocs.css to JavaDoc stylesheet.css for badge styles
...

How was this patch tested?

Manually tested via:

SKIP_PYTHONDOC=1 SKIP_RDOC=1 SKIP_SQLDOC=1 jekyll build

[HyukjinKwon]

cc @srowen, @dongjoon-hyun, @jiangxb1987

[jiangxb1987]

LGTM, pending jenkins

[SparkQA]

Test build #112542 has finished for PR 26228 at commit 17c9985.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[jiangxb1987]

Thanks, merging to master!

[HyukjinKwon]

Thanks all!

[dongjoon-hyun]

Thank you all!