Add Logback's throwable-consuming semantics as an option

[ppkarwasz]

The semantics used to determine the Throwable attached to a log event changed in Logback 1.1.0 (in the fix to LOGBACK-873).

When there are not enough arguments to the log call to fill both the throwable field and the placeholders contained in the message pattern, Logback 1.1.0 and later prefer to fill the throwable field and leave some placeholders empty. Log4j Core does the opposite choice: it first fills all the placeholders and only fills the throwable field if there is something left.

This change allows log4j-slf4j-impl and log4j-slf4j2-impl users to switch between the two behaviors by setting the property log4j2.messageFactory to:

org.apache.logging.slf4j.message.ThrowableConsumingMessageFactory

In this PR two choices have been made:

• the message factory is only included in log4j-slf4j-impl and log4j-slf4j2-impl, since it should be mostly required by Logback users during a transition period. Note that Logback's and Log4j's semantics to deal with throwables agree whenever enough arguments are provided. In a second step users can modify their code using Add recipe to clone an exception argument openrewrite/rewrite-logging-frameworks#141, so that it behaves in the same way in Logback and Log4j Core out-of-the-box. However I can also create a new log4j-message artifact for this.
• no garbage-free version of this factory is provided. SLF4J creates temporary arrays whenever more than 2 arguments are provided. I believe that an additional creation of a ParameterizeMessage instance does not make a difference.

Closes #2363

[vy]

LGTM, thanks for taking care of this @ppkarwasz! 💯
I have two nits:

1. Would you mind explicitly stating in all newly added Java source files something like the following, please?

This class should be identical to its clone in {@code log4j-slf4j2-impl}.
Any changes made here should be reflected to the other one, and vice versa.

2. Would you mind documenting this in the following files, please?
   1. migrate-from-logback.adoc
   2. installation.adoc#impl-logback

[ppkarwasz]

@vy,

1. Would you mind explicitly stating in **all** newly added Java source files something like the following, please?

This class should be identical to its clone in {@code log4j-slf4j2-impl}.
Any changes made here should be reflected to the other one, and vice versa.

I don't think this is necessary. Every time one of log4j-slf4j-impl or log4j-slf4j2-impl is modified, the other one needs to be modified too.

2. Would you mind documenting this in the following files, please?
   
   1. `migrate-from-logback.adoc`
   2. `installation.adoc#impl-logback`

I added some documentation to migrate-from-logback.adoc in f7a6320.
The ThrowableConsumingMessageFactory is only useful for people that migrate from Logback, so I didn't add it to installation.adoc.