[IO-808] more precise Javadoc about when an IllegalArgumentException is thrown

[elharo]

Clarify the circumstances under which an IllegalArgumentException is currently thrown. I think these are all the cases where IO-808 proposes using IOExceptions instead. This is an intermediate step that merely documents what the code currently does. Some of these should be changed. @garydgregory @sebbASF

[garydgregory]

Hello @elharo
Please link to Jira URLs for convenience.

[garydgregory]

@elharo
There are lots of build errors where it looks like you mixed up @link for @code:

...
Error:  /home/runner/work/commons-io/commons-io/src/main/java/org/apache/commons/io/FileUtils.java:2442: error: reference not found
Error:       * @throws IllegalArgumentException if {@link srcFile} is a directory
Error:                                                    ^
...

Run mvn by itself before you push to avoid build errors.

[rho66]

see IO-778 were also IllegalArgumentException is thrown but not documented in Javadoc.