Fix issue #2380: Log messages with insufficient parameters should not throw exception.

[SeasonPanPan]

Fix issue #2380: Log messages with insufficient parameters should not throw exception.

In this PR, I modified the class org.apache.logging.log4j.message.ParameterFormatter.
I deleted the codes about checking placeholderCount and argCount, if they weren't equal, it would throw an IllegalArgumentException.

At the same time, I also modified the corresponding test cases.

Close #2380

@ppkarwasz Please review the codes when you have time.

[vy]

I see several tests being replaced by single-shot examples, please don't. Instead use a @ParameterizedTest and provide several examples providing sufficient coverage. I also would like to see examples where arguments contain Throwables to match against the cases @ppkarwasz stated.

[SeasonPanPan]

@vy @ppkarwasz Done, and added some test cases with the following scenarios:

 * 1. The placeholders are greater than the count of arguments. 
 * 2. The placeholders are less than the count of arguments.  
 * 3. The arguments contains an exception, and the placeholder is greater than normal arguments. 
 * 4. The arguments contains an exception, and the placeholder is less than the arguments. 
 All of these should logged in status logger with WARN level.

But this case with no warn log:

• The arguments contains an exception, and the placeholder count is equal to normal arguments.

[ppkarwasz]

Nice job!

It almost looks good to me, except we need to maintain Log4j semantics (which is the same as Logback < 1.1.0 semantics) for classifying a trailing Throwable as part of the arguments or as "extra" argument.

[ppkarwasz]

Apart from the usage of args.length, it looks good to me.

[SeasonPanPan]

Apart from the usage of args.length, it looks good to me.

Done. Because the argCount might be 0 in ReusableMessage, I made a non-zero judgment in advance.

[ppkarwasz]

@SeasonPanPan

Thank you for your contribution.