Underline alignment regression

[CosmicHorrorDev]

cc @trimental

Just noticed that the PR to add alignment for tables regressed alignment for text vs its underline

Repro

<h1 align="center">Some text</p>

Rendered

You can see that the text is center aligned while the underline is left aligned

This seems to be due to removing the alignment from the Key which was used to set the alignment of the buffer_line. Admittedly I'm not really familiar enough with the renderer to know how to fix things without likely regressing other parts

[trimental]

Yep haha. Currently trying to fix this issue. Getting close to honing in on it but it's a tricky one. Going to need more time to sort it out.