wallet_requestSnaps always show install dialog in different localhost sites

I create two site A and site B in localhost. In site A, I have installed snap A(running in 8080). The snap's config is:

```
{
"version": "0.1.0",
"description": "SnapA",
"proposedName": "SnapA",
"repository": {
"type": "git",
"url": "https://github.com/MetaMask/template-snap-monorepo.git"
},
"source": {
"shasum": "63qRiHOi37RFs/GvzuscNwJ3wmyzz16bpckmJM7VUqI=",
"location": {
"npm": {
"filePath": "dist/bundle.js",
"packageName": "snap-a",
"registry": "https://registry.npmjs.org/",
"iconPath": "images/logo.svg"
}
}
},
"initialPermissions": {
"snap_dialog": {},
"endowment:rpc": {
"dapps": true,
"snaps": true
},
"snap_manageState": {},
"endowment:network-access": {},
"endowment:page-home": {},
"endowment:ethereum-provider": {},
"endowment:cronjob": {
"jobs": [
{
"expression": "*/10 * * * * *",
"request": {
"method": "alert"
}
}
]
}
},
"manifestVersion": "0.1"
}

```

And in site B, I used wallet_requestSnaps to request permission to connect to the snap A, there is always an install dialog to install snap A.

```
const snap = await request({
method: 'wallet_requestSnaps',
params: {
'local:http://localhost:8080': {},
},
});
```

Start by tracing the wallet_requestSnaps handling for local snap requests and how permissions are associated with different localhost sites. Reproduce the two-site setup described in the issue and inspect the existing permission state. Done means an already installed snap does not trigger an install dialog when requested from another localhost site, if that is the intended behavior.

Written by the indexing model from the issue text.