Use texture as shader prop

[jfboeve]

This pull request introduces support for a new beforeDraw lifecycle method in WebGL shaders, allowing developers to bind additional textures and update uniforms immediately before the draw call. It includes updates to the core shader node, WebGL shader node, and documentation, as well as a new example demonstrating how to use this feature.

New Shader Lifecycle Support:

• Added an optional beforeDraw method to the WebGlShaderType interface, which can be used to bind extra textures or update uniforms before each draw call (src/core/renderers/webgl/WebGlShaderNode.ts, src/core/renderers/webgl/WebGlShaderNode.tsR40-R47).
• Implemented logic in WebGlShaderNode and WebGlShaderProgram to call beforeDraw before rendering, and provided a bindTexture helper for texture binding (src/core/renderers/webgl/WebGlShaderNode.ts, [1]; src/core/renderers/webgl/WebGlShaderProgram.ts, [2].

API and Internal Changes:

• Updated CoreShaderNode and WebGlShaderNode to store and manage the beforeDraw function, and track additional textures per draw (src/core/renderers/CoreShaderNode.ts, [1]; src/core/renderers/webgl/WebGlShaderNode.ts, [2].

Documentation:

• Added a new section to the documentation explaining the usage and purpose of the beforeDraw property, including a code example (docs/webgl-shader-types.md, docs/webgl-shader-types.mdR164-R182).

Examples:

• Added a new test example, shader-with-texture-prop.ts, demonstrating how to use the beforeDraw method to bind an additional texture and pass uniforms to a custom shader (examples/tests/shader-with-texture-prop.ts, examples/tests/shader-with-texture-prop.tsR1-R157).

Minor Refactoring:

• Made glw a public property in WebGlShaderProgram to facilitate access from shader nodes (src/core/renderers/webgl/WebGlShaderProgram.ts, src/core/renderers/webgl/WebGlShaderProgram.tsL53-R49).
• Cleaned up unused imports in WebGlShaderProgram.ts (src/core/renderers/webgl/WebGlShaderProgram.ts, src/core/renderers/webgl/WebGlShaderProgram.tsL23-R23).