templates: Add readFile function, skips parsing contents as a template

[asyncmeow]

This is a fix for the issue I created earlier, closes #5552. It's mostly a copy-paste of the include function, but skips the template parsing step to just return the body of the file unmodified.

[CLAassistant]

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[asyncmeow]

Fixed the formatting issues + squashed the two commits together

[mholt]

Cool, this LGTM. I'm just waiting to merge while I try to think of a better name than includeRaw if one exists. :) That's all.

[asyncmeow]

Maybe includeText? Honestly I just did includeRaw since that's what someone mentioned in Discord and I'm not that good at naming 😅

[mholt]

Yeah that's alright. It's not bad, just seems like an afterthought (which it is).

What I should have done is named include eval and then include could be the un-evaluated includer. Sigh.

[francislavoie]

Maybe like readFile or something?

[mholt]

I like readFile -- let's do that!

[francislavoie]

I pushed a commit to rename it, and I made some additional adjustments to the template docs cause I thought it wasn't super clear which functions would render in place and which would just return the buffer.

[mholt]

Thanks, LGTM. (Don't mind the deleted comment; I was thrown off, not realizing that docs for other actions were edited -- I'm not sure why though.) (Edit: D'oh, just now seeing Francis' comment. Sigh.)

I think we can merge this 😃 Thanks for the contribution!