### Godot version

4.0b17

### System information

macOS 13.2

### Issue description

The shader function fma, used by the visual shader UVFunc node generated code:
```
// UVFunc:5
vec2 n_in5p1 = vec2(6.00000, 6.00000);
vec2 n_in5p2 = vec2(0.50000, 0.50000);
vec2 n_out5p0 = fma((UV - n_in5p2), n_in5p1, n_in5p2);
```
Does not seem to be defined in the Compatibility renderer, causing shader compilation to fail if it's used with a lot of errors and debug output (10000+ messages as it prints out a lot of engine shader code?). Ending with the relevant errors:
 ```
drivers/gles3/shader_gles3.cpp:242 - SceneShaderGLES3: Fragment shader compilation failed:
  ERROR: 0:928: Invalid call of undeclared identifier 'fma'
  ERROR: 0:930: Use of undeclared identifier 'm_n_out5p0'
  
  drivers/gles3/shader_gles3.cpp:342 - Method/function failed.
```

Simple shader using fma in Mobile:
![Screenshot 2023-02-08 at 09 52 38](https://user-images.githubusercontent.com/17763524/217483066-fe0feab7-72c4-4db7-a44e-041a1ad93f25.jpg)

Switch to Compatibility renderer:
![Screenshot 2023-02-08 at 09 53 27](https://user-images.githubusercontent.com/17763524/217483149-4fdef308-67cf-40d2-8d4a-d72dc7c85e70.jpg)



### Steps to reproduce

- Start a project in Mobile
- Make a shader where you use the fma function, for example the shader below in the reproduction field. Or a visual shader using the UVFunc node.
- Assign the shader to a shader material and apply this to a visible mesh, observe it renders
- Switch project to Compatibility renderer
- See errors and failed shader compilation

### Minimal reproduction project

Minimal test shader, use in Compatibility renderer:

```
shader_type spatial;

void fragment() {
	vec2 n_in5p1 = vec2(6.00000, 6.00000);
	vec2 n_in5p2 = vec2(0.50000, 0.50000);
	vec2 n_out5p0 = fma((UV - n_in5p2), n_in5p1, n_in5p2);

	ALBEDO = vec3(1,0,0);
}

```
return "model_view_matrix";
}
String VisualShaderNodeBillboard::generate_code(Shader::Mode p_mode, VisualShader::Type p_type, int p_id, const String *p_input_vars, const String *p_output_vars, bool p_for_preview) const {
	String code;
	switch (billboard_type) {
		case BILLBOARD_TYPE_ENABLED:
			code += "	{\n";
			code += "		mat4 __mvm = VIEW_MATRIX * mat4(INV_VIEW_MATRIX[0], INV_VIEW_MATRIX[1], INV_VIEW_MATRIX[2], MODEL_MATRIX[3]);\n";
			if (keep_scale) {
				code += "		__mvm = __mvm * mat4(vec4(length(MODEL_MATRIX[0].xyz), 0.0, 0.0, 0.0), vec4(0.0, length(MODEL_MATRIX[1].xyz), 0.0, 0.0), vec4(0.0, 0.0, length(MODEL_MATRIX[2].xyz), 0.0), vec4(0.0, 0.0, 0.0, 1.0));\n";
			}
			code += "		" + p_output_vars[0] + " = __mvm;\n";
			code += "	}\n";
			break;
		case BILLBOARD_TYPE_FIXED_Y:
			code += "	{\n";
			code += "		mat4 __mvm = VIEW_MATRIX * mat4(INV_VIEW_MATRIX[0], MODEL_MATRIX[1], vec4(normalize(cross(INV_VIEW_MATRIX[0].xyz, MODEL_MATRIX[1].xyz)), 0.0), MODEL_MATRIX[3]);\n";
			if (keep_scale) {
				code += "		__mvm = __mvm * mat4(vec4(length(MODEL_MATRIX[0].xyz), 0.0, 0.0, 0.0), vec4(0.0, 1.0, 0.0, 0.0), vec4(0.0, 0.0, length(MODEL_MATRIX[2].xyz), 0.0), vec4(0.0, 0.0, 0.0, 1.0));\n";
			} else {
				code += "		__mvm = __mvm * mat4(vec4(1.0, 0.0, 0.0, 0.0), vec4(0.0, 1.0 / length(MODEL_MATRIX[1].xyz), 0.0, 0.0), vec4(0.0, 0.0, 1.0, 0.0), vec4(0.0, 0.0, 0.0, 1.0));\n";
			}
			code += "		" + p_output_vars[0] + " = __mvm;\n";
			code += "	}\n";
			break;
		case BILLBOARD_TYPE_PARTICLES:
			code += "	{\n";
			code += "		mat4 __wm = mat4(normalize(INV_VIEW_MATRIX[0]) * length(MODEL_MATRIX[0]), normalize(INV_VIEW_MATRIX[1]) * length(MODEL_MATRIX[0]), normalize(INV_VIEW_MATRIX[2]) * length(MODEL_MATRIX[2]), MODEL_MATRIX[3]);\n";
			code += "		__wm = __wm * mat4(vec4(cos(INSTANCE_CUSTOM.x), -sin(INSTANCE_CUSTOM.x), 0.0, 0.0), vec4(sin(INSTANCE_CUSTOM.x), cos(INSTANCE_CUSTOM.x), 0.0, 0.0), vec4(0.0, 0.0, 1.0, 0.0), vec4(0.0, 0.0, 0.0, 1.0));\n";