Improve intrinsic functions and add json fallback parsing

[satyakigh]

Description

This PR improves how the CloudFormation Language Server parses and handles intrinsic functions (like !If, !Sub, !Ref, Fn::GetAtt, etc.) in both YAML and JSON
templates. It also adds a JSON fallback parser for malformed/incomplete documents.

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Key Changes

1. SyntaxTree.ts - Core parsing improvements

Intrinsic function path handling:

• Refactored YAML tag handling (!If, !Sub, !Ref, etc.) to run independently rather than in an else-if chain
• This ensures both the intrinsic function name AND the parent property are captured in the path
• Added support for flow_node in addition to block_node for YAML intrinsics
• Added check to skip when parent is ERROR node (lets fallback handle malformed trees)

New JSON fallback parser:

• Added pathAndEntityJsonFallback() method (~100 lines) for malformed JSON documents
• Uses text-based stack parsing to infer context when tree-sitter produces ERROR nodes
• Tracks JSON structure ({, }, [, ], :, ,) to build path context
• Enables completions in incomplete JSON templates (e.g., typing a property name)

Minor fix:

• Added handling for cursor after YAML TAG nodes (e.g., !Sub or incomplete !E)

2. LogicalIdReferenceFinder.ts - Simplified reference extraction

• Simplified early-exit checks using text.includes() instead of indexOf()
• Removed separate JsonSub/YamlSub regex patterns - now uses unified SubVariables pattern
• Added !If and Fn::If: pattern matching for YAML
• Unified ${...} variable extraction for both JSON and YAML into single SubVariables regex
• Improved SubVariables regex to capture only the resource name from ${Resource.Attribute} syntax
• Added 'AWS' to CommonProperties exclusion set (filters out AWS::Region, etc.)

[Zee2413]

Would using IntrinsicFunction enum make these more maintainable?

[satyakigh]

A lof of the intrinsic functions are being used here, it was easier to read and follow without using the enums here

[Zee2413]

We are iterating and checking node type twice, once in the condition to enter this scope (line 510) and again to assign tagNode.
Can we search once and continue if not found?

[satyakigh]

Both of these exit early since it just looks for the first child and if we compute this before the if, then the search always runs even if the other conditions might be false. This is only looking for first element so it should be fast enough

[Zee2413]

Was not suggesting to compute before if but rather remove line 510 from if condition, and exit if no tagNode is found after line 512.

[Zee2413]

This 100 line method is getting longer. It would be good to refactor the new Tag change into a method. We can take care of the rest later.

[satyakigh]

This is just moving the existing logic from below to be up top, only the comments are extra