groups attribute is not properly processed

Describe the bug

According to https://makecode.com/defining-blocks#category,

To define your groups, add the groups attribute to your namespace. The groups attribute is an array of group names.

The order in which you define your groups is the order in which the groups will appear in the toolbox flyout

, and it has a sample syntax of the groups attribute:

//% groups=['LED matrix', 'Control flow', 'others']

Unfortunately, that does work.

On https://makecode.com/playground#basic-groups, another syntax is shown:

//% groups="['Fruits', 'Veggies']"

Sadly, that does not work either.

The only syntax that appears to work is as follows:

//% groups='["Fruits", "Veggies"]'

I think either the above samples should amended, or the parser should support all of them.

To Reproduce

1. Go to https://makecode.com/playground#basic-groups
2. Click "Run"
3. Replace //% groups="['Fruits', 'Veggies']" with //% groups=['Fruits', 'Veggies']
4. Click "Run"
5. Replace //% groups=['Fruits', 'Veggies'] with //% groups=["Fruits", "Veggies"]
6. Click "Run"
7. Replace //% groups=["Fruits", "Veggies"] with //% groups='["Fruits", "Veggies"]'
8. Click "Run"

Actual behavior
After Step 2, 4 and 6:

After Step 8: