These are only ever used with ShaderCode instances and nothing else.
Given that, we can convert these helper functions to expect that type of
object as an argument and remove the need for templates, improving
compiler throughput a marginal amount, as the template instantiation
process doesn't need to be performed.
We can also move the definitions of these functions into the cpp file,
which allows us to remove a few inclusions from the ShaderGenCommon
header. This uncovered a few instances of indirect inclusions being
relied upon in other source files.
One other benefit is this allows changes to be made to the definitions
of the functions without needing to recompile all translation units that
make use of these functions, making change testing a little quicker.
Moving the definitions into the cpp file also allows us to completely
hide DefineOutputMember() from external view, given it's only ever used
inside of GenerateVSOutputMembers().
We only use these string streams to output into a final std::string
instance, we don't read into types with them. Because of this, we can
just make use of std::ostringstream, rather than the fully-fledged
std::stringstream.
No behavioral change. This is intended to make the transition to fmt
less noisy in subsequent changes by combining insertions of multiple
string literals into one where applicable.
