feat(block-node): add getFragments method

[ilyamore88]

• Add .getFragments() method for BlockNode
• .getFragment() method of InlineNode returns fragments with their range even if it was called with specific range

[github-actions[bot]]

Coverage report for ./packages/model

St.:grey_question:	Category	Percentage	Covered / Total
🟢	Statements	100%	588/588
🟢	Branches	99.27% (+0.01% 🔼)	136/137
🟢	Functions	99.33% (+0.02% 🔼)	149/150
🟢	Lines	100%	563/563

Test suite run success

346 tests passing in 19 suites.

Report generated by 🧪jest coverage report action from a5f829179ab8b9bbc0f9be2a9e67e5a1197f63a9

[github-actions[bot]]

✅ Mutation testing passed

Report: https://dashboard.stryker-mutator.io/reports/github.com/editor-js/document-model/PR-54

Mutated files

src/EditorJSModel.ts
src/entities/BlockNode/index.ts
src/entities/EditorDocument/index.ts
src/entities/inline-fragments/FormattingInlineNode/index.ts
src/entities/inline-fragments/TextNode/index.ts