fix(compiler-ssr): handle ssr attr fallthrough when preserve whitespace

[edison1105]

close #8072

Summary by CodeRabbit

• Bug Fixes

  • Improved server-side rendering of fallthrough component content when whitespace or comments are present, ensuring consistent output for conditional branches.

• Tests

  • Added coverage verifying whitespace-preserving rendering of fallthrough components with conditional content.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

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Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	100 kB	38 kB	34.2 kB
vue.global.prod.js	159 kB	57.9 kB	51.4 kB

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.9 kB	18.3 kB	16.7 kB
createApp	55 kB	21.3 kB	19.4 kB
createSSRApp	59 kB	23 kB	20.9 kB
defineCustomElement	59.8 kB	22.8 kB	20.8 kB
overall	68.7 kB	26.3 kB	24 kB

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commit: 1d7c440