[simd.creation] Lambda display issues

[hewillk]

The lambda expression here is missing curly braces {}, but LaTeX code seems to be correct. I don't know what happened.

[tkoeppe]

Probably someone types {} instead of \{\}.

[frederick-vs-ja]

N5054 is also misformatted.

This seems like the first time we use lambda in \tcode. Previously we generally use lambdas in codeblock so there wasn't any escaping.

[tkoeppe]

(This is a very common mistake. I try to catch it before merging, but it does slip through every so often.)