Migration: SDoc model: Merge Section, Node, Composite Node into just Node

[stanislaw]

Task

• Start recognizing [[REQUIREMENT]] syntax. backend/sdoc: groundwork for new composite node syntax #2192
• GrammarElement: add support of PROPERTIES/IS_COMPOSITE: True/False
• Make the node template have the buttons for adding a child node. backend/sdoc, UI: enable composite requirements adding #2194
• [[...]] nodes: Validate that start/end tags match. backend/sdoc: prepare model for [[SECTION]] migration #2200
• [[...]] nodes: Validate that the grammar declaration allows such elements. backend/sdoc: document grammar validations for new [[NODE]] syntax #2202
• Migration: SDoc model: Merge Section, Node, Composite Node into just Node #2193
  • Section/Narrative UI style. Header font sizes.
  • Section: What to do with the mandatory STATEMENT field?
  • Node: Anchors from sections.
• backend/sdoc: document_grammar: make TEXT node to have Plain style by default #2244
• Delete Requirement: For composite requirements, also validate that all child nodes recursively. Feature: Handle recursive deletion of sections #1001
• Make SDocSection be a subclass of SDocNode. backend/sdoc: Prepare automatic migration: [SECTION] -> [[SECTION]] #2250
• Double-check the migration of REQ_PREFIX. backend/sdoc: REQ_PREFIX->PREFIX for composite [[NODE]] #2256
• Double-check the migration of LEVEL.
• Migration: [[NODE]]: Remove [COMPOSITE_REQUIREMENT] from codebase #2257
• tests/end2end: create [[SECTION]], deprecate create [SECTION] #2258
• UI: adjust Move Node to [[NODE]] #2259
• Document the migration. docs: document the migration path: [SECTION] -> [[SECTION]] #2260
• [[NODE]] migration: print [SECTION] deprecation message #2261
• Section UID generator. [[NODE]] migration: carry over SECTION reset UID behavior #2263
• docs: update the SDoc markup chapter: [[NODE]]-related updates #2266
• Project statistics: Section-related. Migrate. [[NODE]] migration: extend project statistics and query syntax to support [[SECTION]] #2274.
• [[NODE]] migration: adjust Diff/Changelog, add end-to-end test #2280
• [[NODE]] migration: move node: add missing end2end test  #2283
• Duplicate content in the Document elements.
• Double-check the DEPRECATED: SECTION.
• Task: Update REQUIREMENT_STYLE section in User Guide #2241
• Migrate all Section-related tests that are not available in the node tests group yet.
• Remove all Section-related tests.

Why?

• Closer compatibility to ReqIF which does not have Sections but only recursive nodes.
• First-class support of Composite Requirements in all generators and the UI.
• Remove a lot of duplication between Section and Node because section is just a hardcoded node in many aspects.