Performance issue in QSGShaderEffect::lookThroughShaderCode()

Calling QSGShaderEffect::lookThroughShaderCode() takes a lot of time. For example if a list delegate contains an element with a ShaderEffect, creating this delegate causes two calls to lookThroughShaderCode() one for vertex and one for fragment shader. Both of this calls takes noticeable portion of creation time and affect frame rate.

There may be room for improvement, it should be possible to rewrite the function based on mallocfree const char *'s and no RegExp.