feat: trim invalid chars at start of shader file (such as UTF8 BOM)

[steviegt6]

It would be great to address cryptic errors like this directly from our compiler without worrying too much:
ShopItemHoverFlash.fx(1,1): Error X3000 : Illegal character in shader file

The only issue I foresee is that this produces inconsistent behavior when using another compiler.

[steviegt6]

I'm raising this as absolutely desired to match the capabilities of other community tooling.