feat: add templ elements, and templ block elements

[joerdav]

No description provided.

[joerdav]

@a-h I'm happy that this works as expected now.
Would be good to get your eyes over it first and make sure it's acceptable.
I left callTemplatesExpressions in for backwards compatability, was this right?

[a-h]

Thanks, this is looking good. I've suggested a couple of minor bits and pieces. Nothing major.

[a-h]

Is there a reason to create a variable instead of using ctx directly? I can't see why childrenVar is used, would be good to remove it if possible, just because it's state inside the generator.

[joerdav]

This was to prevent children being used in components that are nested, I separated it into its own context so that only the { children... } further down can access that context.

If that makes sense.

Otherwise if another templElement was rendered in this component it would get the children passed in, which is bad.

[joerdav]

Was thinking of updating the "Write" function of the calltemplate expression to write out the new syntax. So templ fmt would migrate {! render } to @render.