Use a dedicated SDF render-op flag instead of overloading isCoreNode

[Copilot]

CoreTextNode was taking the SDF-specific branch by overriding isCoreNode, which also changed earlier RTT framebuffer selection in bindRenderOp. That coupling could produce incorrect u_resolution / u_pixelRatio for SDF text rendered under an RTT parent.

• What changed

  • Added a dedicated isSdfRenderOp signal on render ops.
  • Switched SDF-specific bind logic in WebGlShaderProgram to use isSdfRenderOp instead of isCoreNode.
  • Restored CoreTextNode to the normal core-node framebuffer path so RTT parent dimensions continue to be used for resolution selection.

• Behavioral impact

  • SDF text keeps its custom shader binding path.
  • RTT resolution/pixel ratio selection continues to follow core-node semantics for text nodes.
  • Render-op reuse remains stable for SDF text under RTT parents.

• Regression coverage

  • Added focused WebGL tests for:
    • SDF text using parent RTT framebuffer dimensions during uniform binding
    • SDF render-op reuse when parent RTT dimensions match

• Illustrative change

  // before
  if (isCoreNode === false && (renderOp as CoreTextNode).sdfShaderProps !== null) {
    // SDF bind
  }
  
  // after
  if (renderOp.isSdfRenderOp === true) {
    // SDF bind
  }

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