25.0.12 Release Prep

[dessina-devasia]

• Update version to 25.0.12-SNAPSHOT (PR#1483)
• Update IntelliJ Support Range in gradle.properties (PR#1485, PR#1487)
• Update platformVersion (Related open YouTrack issue)
• Update ideTargetVersion
• Update the Intellij version to 2025.3 post release
• Update version to 25.0.12
• Add release notes
• Update LSP4IJ tested versions
• Other doc updates (README.md and user-guide.md)

Reference: https://github.com/OpenLiberty/liberty-tools-intellij/pull/1388/files