[Enhancement Proposal] Share login context between Azure CLI and Azure PowerShell

**Is your feature request related to a problem? Please describe.**

Sharing login context between Azure CLI and Azure PowerShell is not supported by now.

**Describe the solution you'd like**

Azure CLI and Azure PowerShell can share their login context so that users can choose to use either command:

| |Azure CLI | Azure PowerShell |
|-|-----------|------------------|
| login | [`az login`](https://docs.microsoft.com/en-us/cli/azure/reference-index?view=azure-cli-latest#az_login) | [`Connect-AzAccount`](https://docs.microsoft.com/en-us/powershell/module/az.accounts/connect-azaccount) |
| change context | [`az account set`](https://docs.microsoft.com/en-us/cli/azure/account?view=azure-cli-latest#az_account_set) | [`Set-AzContext`](https://docs.microsoft.com/en-us/powershell/module/az.accounts/set-azcontext) |

**Additional context**

To share login context, Azure CLI and Azure PowerShell must share 2 things:

| | Azure CLI | Azure PowerShell |
|---------------|---------------------|-----------------------|
| context | `azureProfile.json` | `AzureRmContext.json` |
| token cache | `accessTokens.json` | `TokenCache.dat` |

For token cache, once both migrate to MSAL, `TokenCache.dat` and `accessTokens.json` will be merged into

```
C:\Users\\AppData\Local\.IdentityService\msal.cache
```

so we get shared `msal.cache` out of the box.

But for `AzureRmContext.json` and `azureProfile.json`, it is very hard for Azure CLI to use `AzureRmContext.json` from Azure PowerShell given the internal implementation logic is such different.

Also, Azure CLI faces another issue for tenant/user isolation which should also be addressed first before sharing login context with Azure PowerShell: #15005.

If this is really something we need to achieve, drastic overhaul of Azure CLI and Azure PowerShell is necessary.