Improve LSP Hover and Completion for Reduce Action Bindings

[ehwan]

• Add resolved type information to LSP hover and completion details for reduce action bindings such as data, lookahead, shift, Err, @0, and @$.
• Resolve grammar substitution variables and aliases before displaying types, including %moduleprefix, %userdata, %location, %error / %errortype, and %tokentype.
• Add hover and completion support for mapped symbols used as plain identifiers inside reduce actions.
• Show production-token reference context for mapped symbols, $1 / $2 positional values, and @1 / @2 location references using a caret marker under the referenced RHS token.
• Keep completion documentation aligned with hover documentation for reduce action variables and bindings.

[gemini-code-assist]

Code Review

This pull request enhances the Language Server Protocol (LSP) implementation for RustyLR by providing rich hover information and completion suggestions inside reduce actions. It introduces support for resolving semantic value bindings, positional variables, location references, and GLR control variables (such as data, lookahead, shift, and Err), including resolving types after substitution (e.g., resolving $moduleprefix references). Feedback on the changes includes addressing a stack corruption issue in resolve_provider_stream due to an early return bypassing stack.pop(), and decoupling the collection of default binding types from token references in variables_for_offset to ensure types are always populated when a grammar is available.

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[gemini-code-assist]

In variables_for_offset, the collection of default binding types is incorrectly coupled with the presence of reference (token references). If reference is None (e.g., if reference resolution fails or is not applicable), collect_default_binding_types is never called, meaning default bindings will not have their types populated and won't be suggested in completion. Decouple the two operations so that default binding types are always collected as long as grammar is available.

Suggested change

	if let (Some(grammar), Some(reference)) =
	(&grammar, token_references.get(variables.value_count - 1))
	{
	collect_default_binding_types(
	args,
	grammar,
	pattern,
	&mut variables.value_types,
	);
	collect_default_binding_references(
	pattern,
	reference,
	&mut variables.value_references,
	);
	}
	if let Some(grammar) = &grammar {
	collect_default_binding_types(
	args,
	grammar,
	pattern,
	&mut variables.value_types,
	);
	}
	if let Some(reference) = token_references.get(variables.value_count - 1) {
	collect_default_binding_references(
	pattern,
	reference,
	&mut variables.value_references,
	);
	}