fix: use string manipulation instead of regex to inject esbuild helpers

[fnlctrl]

Description

Fix #14065 lib mode hanging for umd build, by using string manipulation instead of regex

Additional context

The original fix #7948 used regex for string replacement to avoid global esbuild helpers.

It has since caused multiple performance issues #8738 #8099 #10900 #14065, and received numerous attempts #8110 #8741 #10905 at fixing it, but there're still unhandled cases:

• UMD build, minify: true https://stackblitz.com/edit/vitejs-vite-9frvl5?file=vite.config.ts,index.tsx&terminal=build
• UMD build, minify: false https://stackblitz.com/edit/vitejs-vite-z5wdig?file=vite.config.ts,index.ts&terminal=build

I think this shows that regex isn't the right solution in this scenario. It's easier to manipulate the string directly, at the cost of a few extra lines.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[fnlctrl]

@patak-dev @sapphi-red @bluwy would you please review this? We're currently blocked on webpack-to-vite switch due to umd build hanging caused by regex. Let me know if I got anything wrong and I'll fix. Thank you!

[bluwy]

Makes sense to me and looks more performant too. Thanks for the PR!

Will wait for another eye on this before merging.

[Penguinlay]

evanw/esbuild#3322 has been fixed.
CC @sapphi-red @fnlctrl