Issue #3311480 by pdureau, Grimreaper, DuaelFr: Reduce preprocess hooks usage...

Issue #3311480 by pdureau, Grimreaper, DuaelFr: Reduce preprocess hooks usage by adding add_class() & set_attributes() filters

Closes #3395953

added 37 commits

• 2d703620...c1a1cee5 - 27 earlier commits
• 6f50e959 - Issue #3413703 by pdureau: Source plugins: methods naming and interfaces use
• 267d774f - Issue #3413043 by pdureau: Add Adapter plugin type
• 372acb62 - Issue #3395963: path source breaks when default source of a prop type
• b0c17adc - Issue #3395963 by pdureau: Fix select & textfield sources.
• 13e8af35 - Issue #3413703 by just_like_good_vibes: Fix typing in Source Plugin Manager & Form Builder
• 80dcb5b1 - Issue #3395954: ComponentConverter, move library & layout properties to dedicated methods
• 3195f9e4 - ISSUE-3395953: Add initial form element
• 967fa96c - ISSUE-3395953: Merge 2.0 branch.
• d4feddd6 - ISSUE-3395953: Fix merge errors.
• f11593ea - ISSUE-3395953: Update docs

Compare with previous version

changed target branch from 8.x-1.x to 2.0.x