refactor: remove optional chaining

[skirtles-code]

Based on #4882 (comment), I believe optional chaining is avoided due to its impact on bundle size. Some recent changes have used the ?. operator, so I have removed them here.

I have only removed instances that had an impact on the size of vue.global.prod.js. Code for SSR or tests or dev hasn't been changed. While some of the replacement code looks a bit verbose, I have confirmed that each change does reduce the size of the unzipped vue.global.prod.js.

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	90.7 kB (-52 B)	34.5 kB (-34 B)	31.1 kB (+3 B)
vue.global.prod.js	148 kB (-158 B)	53.7 kB (-92 B)	48 kB (-99 B)

Usages

Name	Size	Gzip	Brotli
createApp	50.7 kB (-15 B)	19.8 kB (-10 B)	18.1 kB (-14 B)
createSSRApp	54.1 kB (-15 B)	21.2 kB (-10 B)	19.3 kB (-12 B)
defineCustomElement	53 kB (-15 B)	20.6 kB (-10 B)	18.8 kB (-32 B)
overall	64.4 kB (-55 B)	24.9 kB (-32 B)	22.6 kB (-9 B)