`az deployment what-if` incorrectly quotes string values

**Bicep version**
Bicep CLI version 0.3.255 (589f0375df)

**Describe the bug**

When doing a `what-if` deployment through the AZ CLI, changed strings are listed with double quotes. However bicep only supports single quotes, so I'd expect these to be single quoted

```
~ Microsoft.Web/sites/SITE-NAME [2020-06-01]
+ properties.siteConfig.http20Enabled: true
+ properties.siteConfig.linuxFxVersion: "Docker|nginx:alphine"
+ properties.siteConfig.localMySqlEnabled: false
+ properties.siteConfig.netFrameworkVersion: "v4.6"
```

**To Reproduce**

```
az deployment sub what-if sample.bicep
```

Run `az deployment sub what-if sample.bicep` using the reported scenario and compare the rendered values. Trace the what-if output formatting for changed string properties, then verify that values such as `Docker|nginx:alphine` and `v4.6` use Bicep-compatible single quotes and that the existing boolean formatting remains unchanged.

Written by the indexing model from the issue text.