feat: improve ABNF grammar clarity and inline all secondary grammars

[char0n]

Summary

• Add $self expression support (new in Arazzo 1.1.0)
• Add $inputs/$outputs JSON Pointer support (e.g., $inputs.customer#/firstName)
• Inline all secondary grammars ($steps, $workflows, $sourceDescriptions, $components) into the primary grammar, eliminating two-pass parsing
• Extract shared identifier and identifier-strict rules to reduce duplication
• Adapt json-pointer to exclude { and } from unescaped, fixing the embedded expression extraction limitation for body expressions and all other expressions with JSON pointers
• Require explicit component types (parameters/successActions/failureActions)
• Update README with current grammar, examples, and removal of the "known limitation" note

This PR was created as a verification of the proposed ABNF grammar changes in OAI/Arazzo-Specification#454. During implementation, several issues with the spec PR were identified:

1. unescaped in json-pointer still includes { and } — breaks embedded expression parsing; we fix this by excluding them
2. Single identifier rule is too broad — the spec PR uses one rule for both IDs (no dots) and field names (with dots); we use identifier and identifier-strict to respect the spec's different constraints
3. source-descriptions-reference is too restrictive — the spec PR constrains it to identifier, but operationIds in OpenAPI are unconstrained strings; we keep 1*CHAR

Resolves: OAI/Arazzo-Specification#424, OAI/Arazzo-Specification#425, OAI/Arazzo-Specification#426, OAI/Arazzo-Specification#428

Test plan

• All 152 tests pass
• New test fixtures for $self, $inputs/$outputs with JSON Pointer, dotted/hyphenated/underscored names
• Extract tests updated: body expressions with JSON pointers now work in embedded context
• Validation tests updated: {/} in JSON pointer paths now correctly rejected
• Snapshot tests updated for new CST/AST node structure

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR updates the Arazzo runtime expression grammar and translators to support newer spec features and simplify parsing by inlining formerly secondary grammars.

Changes:

• Add $self support and JSON Pointer support for $inputs/$outputs.
• Inline $steps/$workflows/$sourceDescriptions/$components parsing into the primary grammar (eliminating two-pass parsing) and introduce shared identifier rules.
• Adjust JSON Pointer unescaped handling to address embedded-expression extraction ambiguity; update tests, fixtures, and README accordingly.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
test/test.js	Updates validation expectations for {/} in JSON Pointer paths.
test/parse/translators/snapshots/CSTTranslator.js.snap	Updates CST snapshots to reflect new reference node structure.
test/parse/translators/snapshots/ASTTranslator.js.snap	Updates AST snapshots for revised node shapes (e.g., steps/workflows/components).
test/parse/snapshots/cst-corpus.js.snap	Refreshes CST corpus snapshots for new grammar structure and new expressions.
test/parse/snapshots/ast-corpus.js.snap	Refreshes AST corpus snapshots (adds $self, pointers on inputs/outputs, renamed fields).
test/fixtures/expressions-valid.js	Adds new valid expression fixtures ($self, pointers, dotted/hyphenated identifiers).
test/extract.js	Updates extraction tests to confirm embedded body expressions with JSON pointers now extract correctly.
src/parse/translators/CSTTranslator.js	Aligns CST callbacks with the new inlined grammar rules.
src/parse/translators/ASTTranslator/transformers.js	Removes secondary parsing and maps new CST node types directly to updated AST shapes; adds $self.
src/grammar.js	Regenerated grammar output reflecting inlined rules and updated JSON Pointer ranges.
src/grammar.bnf	Updates the source ABNF (primary change set) including inlined references and identifier rules.
README.md	Updates documented ABNF and examples; removes previous JSON-pointer extraction limitation.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.