Add indentation checking by Checkstyle

[jody]

Insert an "Indentation" checking module into jp_checks.xml

Suggested parametric values are: basicOffset (4), caseIndent (4), and LineWrappingIndentation (8).

[jody]

See: https://checkstyle.sourceforge.io/checks/misc/indentation.html

Something like the following might go within the "TreeWalker" module.

<module name="Indentation">
    <property name="basicOffset" value="4"/>
    <property name="caseIndent" value="4"/>
   ︙
    <property name="lineWrappingIndentation" value="8"/>
</module>