[SPARK-21210][DOC][ML] Javadoc 8 fixes for ML shared param traits

[MLnick]

PR #15999 included fixes for doc strings in the ML shared param traits (occurrences of > and >=).

This PR simply uses the HTML-escaped version of the param doc to embed into the Scaladoc, to ensure that when SharedParamsCodeGen is run, the generated javadoc will be compliant for Java 8.

How was this patch tested?

Existing tests

[MLnick]

cc @HyukjinKwon@srowen

[HyukjinKwon]

Just as a little side note, actually, while fixing some javadoc at that time, I realised that even > and < are not actually rendered pretty - #16013 (comment) but I guess here these documentation is privates not exposed in Javadoc where the rendering was problematic. So, I think this's not a big deal here and the change looks minimised and clean.

LGTM.

[SparkQA]

Test build #78637 has finished for PR 18420 at commit 9c24515.

• This patch fails due to an unknown error code, -10.
• This patch merges cleanly.
• This patch adds no public classes.

[MLnick]

@HyukjinKwon true it is private. But there is the possibility that (at least some of) these shared params are made public in the future. So worth doing I guess.

[MLnick]

Jenkins retest this please

[SparkQA]

Test build #78684 has finished for PR 18420 at commit 9c24515.

• This patch fails PySpark pip packaging tests.
• This patch merges cleanly.
• This patch adds no public classes.

[MLnick]

Will wait for pip tests to get sorted out before trying again!

[HyukjinKwon]

Sad ... I guess it fails only on some environments in Jenkins BTW.

[SparkQA]

Test build #3817 has finished for PR 18420 at commit 9c24515.

• This patch fails PySpark pip packaging tests.
• This patch merges cleanly.
• This patch adds no public classes.

[MLnick]

Jenkins retest this please

[SparkQA]

Test build #78885 has finished for PR 18420 at commit 9c24515.

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

[srowen]

Merged to master/2.2