Evaluate using lexical-binding if the file is lexically scoped

[phikal]

I have code in my init.el that requires lexical scoping, and it could not be evaluated correctly without passing setting lexical when calling eval.

This patch uses the buffer-local value of lexical-binding to invoke eval correctly.

[phikal]

And as a side note, while debugging I ended up simplifying the code a bit, but there too many changes to make a clean sequence of commits. Ultimately, I just grouped them all into one big dummy commit, and if you are interested, I could extract certain changes and propose them as separate push requests.

[phikal]

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