PERF: Extensive constant propagation

[LifeIsStrange]

Clear and concise description of the problem

Constant folding (propagation) is a popular optimization https://en.m.wikipedia.org/wiki/Constant_folding

Many things can be constant folded at compile time, an important one are CSS calc() expressions

Suggested solution

This is solved by https://github.com/postcss/postcss-calc
However most people are not even aware of the existence of this library.
As such it would be a nice optimization if vite leveraged internally this lib in order to perform css Calc constant folding for free to users.

Note that esbuild might support this one day
evanw/esbuild#1607

Alternative

What other things can be constant folded at compile time?

Also this is desired for production but is it also desired for dev?

Additional context

No response

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[sodatea]

Now that esbuild is going to support this feature, we should leave it to esbuild, for separation of concerns.