SCons: Add method to generate raw cstrings

[Repiteo]

Through the use of raw strings, generated text that was previously handled as binary can now be displayed without compromise. This not only significantly decreases filesize of generated files, but it makes debugging quite a bit easier thanks to the ease in which this information can be parsed. Currently only applied to the shader/svg generators, but this has the potential to be expanded to more core files if desired.

[Calinou]

Tested locally, it works as expected.

Note that while the generated source files are smaller, the resulting binary size is mostly unaffected (-32 bytes for an optimized stripped Linux x86_64 editor build with this PR).

[akien-mga]

Thanks!

[TheSofox]

I've been having build errors that originated from this PR. Essentially build would fail with repeated error: .\servers/rendering/renderer_rd/shaders/effects/fsr2/fsr2_accumulate_pass.glsl.gen.h(13): fatal error C1091: compiler limit: string exceeds 65535 bytes in length

With the help of other Godot developers, I was able to locate and finally fix this issue.

I was on Windows 10, using Microsoft Visual Studio Community 2019 Version 16.10.2 as the compiler (via scons) when I had the problem. Simply updating Visual Studio fixed it. (Help -> Check for Updates in Visual Studio). It's now on Version 16.11.39 and Godot is compiling fine.

Leaving this message for anyone else who may be encountering a similar issue.