feat(developer): Checks when adding layer name on "Code" panel

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

In Keyman Developer, in the Touch layout interface, the `Add` layer feature does not permit non-Roman letters in the layer name, when letters of other scripts are used the following error message appears (see also the attached screenshot):

```
Layer name must contain only alphanumerics, underscore, and hyphen.
```

However, the user can add a temporary name, switch to the "Code" panel, and replace the temporary name with the desired non-Roman name without issue.

 Developer

### Describe the solution you'd like

The JSON spec does not have the alphanumeric limitation for attribute values. I would like the feature to check validity against a JSON API, and report an error to the user as applicable.

### Describe alternatives you've considered

_No response_

### Related issues

_No response_

### Keyman apps

- [ ] Keyman for Android
- [ ] Keyman for iPhone and iPad
- [ ] Keyman for Linux
- [ ] Keyman for macOS
- [ ] Keyman for Windows
- [X] Keyman Developer
- [ ] KeymanWeb
- [ ] Other - give details at bottom of form

### Keyman version

15.0.273

### Operating system

Windows 11

### Device

Windows Laptop

### Target application

N/A

### Browser

N/A

### Keyboard name

N/A

### Keyboard version

N/A

### Language name

N/A

### Additional context

_No response_

No files, tests, or entry points are identified in the report. Locate the Touch layout Add-layer validation and compare it with the Code panel's JSON attribute validation. Done means valid non-Roman layer names are accepted and invalid values produce an appropriate error.

Written by the indexing model from the issue text.