Parser: Use location-based detection for ERB control types

[marcoroth]

This commit improves the parser's control type detection by comparing keyword locations instead of relying solely on AST node structure.

This template:

<% if value %>
<% elsif items.any? { |item| item.true? } %>
<% end %>

Now gets correctly parsed as:

@ DocumentNode (location: (1:0)-(3:9))
├── errors: []
└── children: (1 item)
    └── @ ERBIfNode (location: (1:0)-(3:9))
        ├── errors: []
        ├── tag_opening: "<%" (location: (1:0)-(1:2))
        ├── content: " if value " (location: (1:2)-(1:12))
        ├── tag_closing: "%>" (location: (1:12)-(1:14))
        ├── statements: (1 item)
        │   └── @ HTMLTextNode (location: (1:14)-(2:0))
        │       ├── errors: []
        │       └── content: "\n"
        │   
        ├── subsequent: 
        │   └── @ ERBIfNode (location: (2:0)-(3:0))
        │       ├── errors: []
        │       ├── tag_opening: "<%" (location: (2:0)-(2:2))
        │       ├── content: " elsif items.any? { |item| item.true? } " (location: (2:2)-(2:42))
        │       ├── tag_closing: "%>" (location: (2:42)-(2:44))
        │       ├── statements: (1 item)
        │       │   └── @ HTMLTextNode (location: (2:44)-(3:0))
        │       │       ├── errors: []
        │       │       └── content: "\n"
        │       │   
        │       ├── subsequent: ∅
        │       └── end_node: ∅
        │       
        └── end_node: 
            └── @ ERBEndNode (location: (3:0)-(3:9))
                ├── errors: []
                ├── tag_opening: "<%" (location: (3:0)-(3:2))
                ├── content: " end " (location: (3:2)-(3:7))
                └── tag_closing: "%>" (location: (3:7)-(3:9))

Previously the elsif was treated as ERBBlockNode causing the <% end %> to be consumed for the ERBBlockNode:

@ DocumentNode (location: (1:0)-(3:9))
├── errors: []
└── children: (1 item)
    └── @ ERBIfNode (location: (1:0)-(3:9))
        ├── errors: (1 item)
        │   └── @ MissingERBEndTagError (location: (1:0)-(1:14))
        │       ├── message: "`<% if %>` started here but never closed with an end tag. The end tag may be in a different scope."
        │       └── keyword: "`<% if %>`"
        │   
        ├── tag_opening: "<%" (location: (1:0)-(1:2))
        ├── content: " if value " (location: (1:2)-(1:12))
        ├── tag_closing: "%>" (location: (1:12)-(1:14))
        ├── statements: (2 items)
        │   ├── @ HTMLTextNode (location: (1:14)-(2:0))
        │   │   ├── errors: []
        │   │   └── content: "\n"
        │   │   
        │   └── @ ERBBlockNode (location: (2:0)-(3:9))
        │       ├── errors: []
        │       ├── tag_opening: "<%" (location: (2:0)-(2:2))
        │       ├── content: " elsif items.any? { |item| item.true? } " (location: (2:2)-(2:42))
        │       ├── tag_closing: "%>" (location: (2:42)-(2:44))
        │       ├── body: (1 item)
        │       │   └── @ HTMLTextNode (location: (2:44)-(3:0))
        │       │       ├── errors: []
        │       │       └── content: "\n"
        │       │   
        │       └── end_node: 
        │           └── @ ERBEndNode (location: (3:0)-(3:9))
        │               ├── errors: []
        │               ├── tag_opening: "<%" (location: (3:0)-(3:2))
        │               ├── content: " end " (location: (3:2)-(3:7))
        │               └── tag_closing: "%>" (location: (3:7)-(3:9))
        │   
        ├── subsequent: ∅
        └── end_node: ∅

Resolves #857