fix: the value of display is sometimes incorrect with v-show

[zh-lx]

a optimize about #10161，close #10151 and won't lead to the issue in #10294

For an element with v-show, when its style changes, el[vShowOldKey] is assigned as style.display, regardless of whether display exists in the style. If v-show === false and there is no display in style, the value of style.display is 'none' at this time, so el[vShowOldKey] will also be incorrectly assigned as 'none'.

The correct logic should be: el[vShowOldKey] = style.display only when display exists in the next style; otherwise, el[vShowOldKey] = ''.

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	90.4 kB (+121 B)	34.4 kB (+54 B)	31 kB (+34 B)
vue.global.prod.js	148 kB (+121 B)	53.7 kB (+50 B)	48 kB (+81 B)

Usages

Name	Size	Gzip	Brotli
createApp	50.5 kB (+90 B)	19.7 kB (+47 B)	18 kB (+39 B)
createSSRApp	53.8 kB (+90 B)	21.1 kB (+45 B)	19.2 kB (+79 B)
defineCustomElement	52.8 kB (+90 B)	20.5 kB (+51 B)	18.7 kB (+26 B)
overall	64.2 kB (+90 B)	24.8 kB (+42 B)	22.5 kB (+88 B)

[zh-lx]

@yyx990803 I think this is a correct fix about #10294? If just revert #10161, the issue about #10151 also will reproduce.