feat(microsyntax): introduce structured microsyntax grammar for structural directives

[albaniosi]

Summary

Replaces the ad-hoc structural_expression / structural_declaration / structural_assignment grammar nodes with a new, purpose-built microsyntax grammar that more precisely models the Angular structural directive microsyntax language.

This also fixes a small bug where naked & characters in text nodes would break the parser. (which in theory is correct by the HTML specification, but is ignored in reality by all parsers and renderers)

Motivation

The previous grammar did not model the possible syntax of Angulars microsyntax for directives very well. For example:

• optionality of the delimiters (,/; - e.g. *ngIf="someCondition else elseBlock")
• *myDirective="let t = x; prefix: 'test.something.asdfasdfasdfdfdf'" (this completly broke the whole following pasing)
• *ngIf="someCondition; then thenBlock else elseBlock"
• *ngFor="let item; of: items trackBy (a, v) => test(a, v)"
• and more

I use Zed whose angular plugin uses this. The parsing was resulting in completely broken files, so i fixed it locally for me. But I thought this might be useful for the project in general.

I hope this helps and I am happy to alter my code to comply with your wishes and standards if possible.

Changes

Grammar (grammar.js)

• Removed structural_expression, structural_declaration, structural_assignment, _else_template_expression, and _context_expression.
• Added a microsyntax subtree:
  • microsyntax — top-level container for the full directive value
  • microsyntax_anonymous_binding — the primary/leading expression (e.g. items, condition ? a : b)
  • microsyntax_binding — any subsequent named binding (dispatches to one of the three below)
  • microsyntax_keyword_binding — reserved keywords (else, then, of) with an optional expression and alias
  • microsyntax_variable_declaration — let name = value / let name declarations
  • microsyntax_property_binding — arbitrary identifier bindings with an expression
• Fixed the text rule to accept a bare & as a fallback, preventing parse failures on ampersands in template text.
• Added conflict resolutions for [$._any_expression, $.arguments], [$.expression, $.arguments], and [$.microsyntax_property_binding, $._primitive].

Highlights (queries/highlights.scm)

• Removed the now-obsolete structural_assignment operator highlight rule.

Tests (test/corpus/structural-directives.txt)

• Migrated all existing corpus cases from structural_expression / structural_declaration nodes to the new microsyntax_* node hierarchy.
• Added comprehensive new corpus cases covering:
  • Primary bindings (identifier and full expression forms)
  • let variable declarations with and without initializers
  • Keyword bindings (else, then, of) with aliases
  • Property bindings
  • Delimiter-less forms
  • Mixed / edge-case combinations

Breaking Change

Any downstream consumers (syntax highlighting, queries, linters) that reference structural_expression, structural_declaration, or structural_assignment nodes will need to be updated to use the new microsyntax_* node names.