native_posix & CONFIG_NATIVE_APPLICATION deprecation plan

[aescolar]

Background

• In 3.5 native_sim was introduced
• In 3.6 native_sim replaced native_posix as the default native simulation target, and users were recommended to switch.
• 3.7 is an LTS => no major changes

Plan

• 4.0: native_posix is deprecated but remains testable by twister (otherwise it would be untested and unsupported for 2 releases)
• 4.1
  • CONFIG_NATIVE_APPLICATION is deprecated
  • CONFIG_NATIVE_SIM_NATIVE_POSIX_COMPAT default is switched to n and deprecated
• 4.2: native_posix is removed
• 4.3:
  • CONFIG_NATIVE_APPLICATION is removed together with the if'ery to support it => out of tree boards based on it stop working.
  • CONFIG_NATIVE_SIM_NATIVE_POSIX_COMPAT is removed

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Related to #58305 & #65059

[aescolar]

CC @carlescufi @jori-nordic @PerMac @daor-oti @wopu-ot @kartben