### Why are the changes needed?
In most of our docs, you can click on a heading to immediately get an anchor link to that specific section of the docs. This is very handy when you are reading the docs and want to share a link to a specific part.
The SQL function docs are lacking this. This PR adds this convenience to the SQL function docs.
Here's the impact on the generated HTML.
Before this PR:
```html
<h3 id="array_join">array_join</h3>
```
After this PR:
```html
<h3 id="array_join"><a class="toclink" href="#array_join">array_join</a></h3>
```
### Does this PR introduce any user-facing change?
No.
### How was this patch tested?
I built the docs manually and reviewed the results in my browser.
Closes#27585 from nchammas/SPARK-30832-sql-doc-headers.
Authored-by: Nicholas Chammas <nicholas.chammas@gmail.com>
Signed-off-by: Sean Owen <srowen@gmail.com>
## What changes were proposed in this pull request?
This generates a documentation for Spark SQL built-in functions.
One drawback is, this requires a proper build to generate built-in function list.
Once it is built, it only takes few seconds by `sql/create-docs.sh`.
Please see https://spark-test.github.io/sparksqldoc/ that I hosted to show the output documentation.
There are few more works to be done in order to make the documentation pretty, for example, separating `Arguments:` and `Examples:` but I guess this should be done within `ExpressionDescription` and `ExpressionInfo` rather than manually parsing it. I will fix these in a follow up.
This requires `pip install mkdocs` to generate HTMLs from markdown files.
## How was this patch tested?
Manually tested:
```
cd docs
jekyll build
```
,
```
cd docs
jekyll serve
```
and
```
cd sql
create-docs.sh
```
Author: hyukjinkwon <gurwls223@gmail.com>
Closes#18702 from HyukjinKwon/SPARK-21485.
