Preprocessor to resolve ifdefs is applied to shader programs

[mvaligursky]

A new private class is added to preprocess defines and ifdefs in the shader with the goal of removing unused code. This is a first preparation step. Following steps will further modify the shader code, in order to convert uniforms to uniform blocks.

New (private) API:

/**
 * Run c-like proprocessor on the source code, and resolves the code based on the defines and ifdefs
 *
 * @param {string} source - The source code to work on.
 * @returns {string|null} Returns preprocessed source code.
 */
static Preprocessor.run(source) {

Note - Simple expression evaluation only is supported for ifdefs, handles cases:

• expression
• defined(expression)
• !defined(expression)

It does not handle more complex cases, which would require more complex system:

• defined(A) || defined(B)
  And so few use cases in the shaders were converted to the supported format.

Unit test has also been added.

Additionally, Debug logging functionality has been extended with trace function.
New (private) API (and also examples of use):

Debug.setTrace(`Preprocessor`, true);
Debug.trace(`Preprocessor`, "message")

and this is displayed in the console:
[Preprocessor] message

[yaustar]

Does this affect the sourcemap generation?

[mvaligursky]

Does this affect the sourcemap generation?

This is only used to process shaders in memory .. so no.

[willeastcott]

This is definitely something for @slimbuck to review - I'll pass.

[mvaligursky]

Updates based on comments @slimbuck
@willeastcott - could you please look at the Debug.trace part I added.

[slimbuck]

We'll probably update the preprocessor over time, but this is a reasonable first pass.