feat(preset-mini)!: update content-x and change handler type

[chu121su12]

This PR changes the behavior introduced in #1717

It turns out [raw:x] syntax that uses space will be difficult (never?) to get matched anywhere. So the behaviour is updated in this PR, such that:

• [raw:x] is removed but may be re-introduced if needed.
• [string:x] will produce an almost equal value to the original x, only replacing unescaped _ to space.
• [quoted:x] is special case that (as of current css spec) would only be useful for content property. This is [string:x] as above with additional quoting with ". This would replace following rule:

  unocss/packages/preset-mini/src/_rules/static.ts

  Line 72 in d2b022d

  [/^content-\[(.+)\]$/, ([, v]) => ({ content: `"${v}"` })],

• The regular bracket syntax for content-[x] is still avaiable but now behaves like regular bracket

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