Pie: showData Decimals

`showData` prints values with `String(value)`: no thousands separators, and `42.10` becomes `42.1`.

pie-showdata-decimals.mmd
pie showData title Revenue by region
  "North" : 2500000.75
  "South" : 1000000
  "East" : 42.10
  "West" : 0.5
Output
Pie chart, Zombie Mermaid 71% 29% Revenue by region North [2500000.75] South [1000000] East [42.1] West [0.5]

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