bug: glslc -E does not escape newlines in string literals

Pretty straight forward to explain. preprocessing with `glslc -E` does not escape newlines in string literals when re-printing the string literal. This results in string literals breaking the source if they're used.

Minimal reproducible example:
```
~> cat shader.glsl
#version 450
#extension GL_EXT_debug_printf : enable

int main(){
debugPrintf("with Newline\n");
}

~> glslc -E shader.glsl
#version 450
#extension GL_EXT_debug_printf : enable

int main() {
debugPrintf("with Newline
");
}

~> glslc --version
shaderc v2023.8 v2025.3
spirv-tools v2025.3 v2022.4-833-g33e02568
glslang 11.1.0-1253-gefd24d75

Target: SPIR-V 1.0
```