fsServe checks break on Windows

[mangowh]

Describe the bug

The new 2.3.0 fsServe configuration and their relative checks do not work quite well on Windows! In a workspace setup, where the vite app is itself an inner package, path checks fails.

At this line

vite/packages/vite/src/node/server/middlewares/static.ts

Line 110 in bdc1ea3

if (!url.startsWith(serveRoot + path.posix.sep)) {

.startsWith break because posix separators do not match windows separators

I'm gonna try to patch this in a PR, wish me luck

System Info

  System:
    OS: Windows 10 10.0.19042
    CPU: (8) x64 Intel(R) Core(TM) i7-8565U CPU @ 1.80GHz 
    Memory: 3.34 GB / 15.78 GB
  Binaries:
    Node: 15.12.0 - C:\Program Files\nodejs\node.EXE      
    Yarn: 1.22.5 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 7.12.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: 90.0.4430.93
    Edge: Spartan (44.19041.906.0), Chromium (90.0.818.56)
    Internet Explorer: 11.0.19041.1

Used package manager: npm

Logs

[vite] Internal server error: The request url "C:\MONOREPO_ROOT\node_modules\bootstrap-icons\font\fonts\bootstrap-icons.woff?231ce25e89ab5804f9a6c427b8d325c9" is outside of vite dev server root "C:/MONOREPO_ROOT".
[dev:frontend]       For security concerns, accessing files outside of workspace root is restricted since Vite v2.3.x. 
[dev:frontend]       Refer to docs https://vitejs.dev/config/#server-fsserveroot for configurations and more details.
[dev:frontend]       at ensureServingAccess (C:\MONOREPO_ROOT\node_modules\vite\dist\node\chunks\dep-c9ea388d.js:57841:15)

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[mangowh]

Probably fixed by #3350

[mangowh]

Proposed draft fix: #3360