Remove AttributeValueSyntax.(Try)GetRawText and move raw-text projection to Semantics.AttributeValue

[jonathanvdc]

Description

AttributeValueSyntax currently exposes (Try)GetRawText to project syntax nodes into preserved raw text:

public abstract bool TryGetRawText(out RawSyntaxText? rawText);

public RawSyntaxText GetRawText()
{
    if (TryGetRawText(out var rawText))
    {
        return rawText!;
    }

    throw new System.InvalidOperationException("This attribute value does not provide a raw syntax-text projection.");
}

This mirrors the same layering issue seen with operation bodies (#13): syntax is being used to recover a semantic projection (raw text), and the API encourages consumers to depend on syntax shape rather than semantic structure.

Additionally, GetRawText() is exception-prone and presents an unsafe API surface.

Proposed Change

Remove AttributeValueSyntax.TryGetRawText(...) and AttributeValueSyntax.GetRawText().

Instead, introduce a method or property on Semantics.AttributeValue that provides raw-text projection where applicable.

This semantic API should:

• return preserved raw syntax text when available, or
• make the absence of raw text explicit (e.g., via nullability or a Try... pattern—decision left to implementation)

Motivation

• Raw-text projection is a semantic concern, not a syntactic one
• Avoids exposing exception-prone APIs on syntax nodes
• Encourages consumers to work with Semantics.AttributeValue instead of probing syntax
• Aligns with the direction of removing projection helpers from syntax types
• Improves separation of concerns between syntax and semantics

Expected Usage After Change

Before:

var raw = attributeValueSyntax.GetRawText();

After (example direction):

if (attributeValue.TryGetRawText(out var raw))
{
    // use raw
}

or:

var raw = attributeValue.RawText; // nullable or optional

Scope

• Remove:
  • AttributeValueSyntax.TryGetRawText(...)
  • AttributeValueSyntax.GetRawText()
• Add a raw-text projection API to Semantics.AttributeValue
• Update all call sites to use the semantic API instead of syntax
• Ensure generators (if applicable) do not depend on syntax-level raw-text extraction

Benefits

• Eliminates exception-prone APIs from syntax layer
• Improves architectural clarity (syntax vs semantics)
• Reduces misuse of syntax as a semantic data source
• Moves toward a more consistent API design across the codebase

Notes

• The new API should clearly communicate when raw text is unavailable
• Consider whether raw-text preservation needs to be optional or guaranteed for certain attribute kinds
• Audit for any other syntax-level projection helpers that should follow the same pattern