[MS8] Branch `main` overhaul #3

[ppkarwasz]

This story aims to overhaul main (targeting Log4j version 3.0.0) branch as a follow up of #1969 and #2016.

Removal of deprecated features

main, since it is forked from 2.x, contains several features and modules that are suitable to be dropped. Since this is a backward incompatible change, we cannot implement this for 2.x. main, targeting 3.0.0, i.e., a new major version release, is a good opportunity for this. Following changes are mostly related with that.

• Remove ThreadLocals.enable property in main #2105
• Remove DefaultLogEventFactory (b338d07)
• Remove Supplier #2175
• Remove log4j-layout-jackson and log4j-layout-jackson-xml #2198
• Remove ineffective tests #2209
• Deprecate StatusConsoleListener filters #2226
• Remove JMX support #2228
• Remove log4j-jcl and log4j-appserver modules #2257

Split functionality to dedicated modules

2.x used to combine several features in one module: log4j-core. This imposes, next to a greater surface for potential vulnerabilities, several disadvantages for those who only need a subset of these offered features. Here we try to improve this experience by moving certain functionalities to their own dedicated modules.

• Consider moving recyclers to log4j-core #2106
• move asynchronous logging to log4j-async
  • Move async support to log4j-async-logger #2241
  • Add general ConfigurationExtension mechanism  #2230
  • Move production code to log4j-async-logger #2248

Port changes from 2.x

main was forked ~6 years ago from 2.x. In the meantime, thousands of improvements were introduced to 2.x and sadly a majority of these were not ported to main. Put another way, main contains several issues that were already fixed in 2.x. Below shared items are related with porting such changes from 2.x to main.

• Port log4j-1.2-api changes from 2.x #2188
• Port log4j-api changes from 2.x #2208
• Restore compatibility of Log4j API #2203
• log4j-appserver (75ab3ae)
• log4j-csv ✔️
• log4j-docker (788ec71)
• log4j-flume-ng (846f354, ca6f923)
• log4j-gctests (245da43)
• log4j-iostreams (4bd7e19)
• log4j-jcl (40f1bde, a863232, b8fb8c8)
• log4j-jdbc (14013cd)
• log4j-jdbc-dbcp2 (2b0ba72)
• log4j-jndi (cf4b39e, 986a716)
• log4j-jndi-test (c5680fe, bac23ba)
• log4j-layout-template-json & log4j-layout-template-json-test (027009e, 923a43e, 3254858, b1113c7)
• log4j-osgi (e25c308, 496951e, 125f505, e3a2559)
• Port log4j-osgi-test changes from 2.x #2187

Miscellaneous improvements

In accordance with Boy Scout Rule, things we have improved along the way:

• Website & changelog (e6044c9, 6f1f129)