Change the implementation in string a number in the string pre-built function

[cosmicshuai]

Currently, the string pre-built function does not always work correctly for numeric inputs.
for example: string(1.22, 'de-DE') returns 1.22. It is not the same as the result of C#.

So I switched the toLocaleString() to d3-format in the string function while a numeric input passed.
With the change, now string(1.22, 'de-DE') will return: 1,22

[coveralls]

Pull Request Test Coverage Report for Build 529473685

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.002%) to 84.679%

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Files with Coverage Reduction	New Missed Lines	%
libraries/adaptive-expressions/src/builtinFunctions/string.ts	2	84.78%

Totals
Change from base Build 529161273:	-0.002%
Covered Lines:	18208
Relevant Lines:	20514

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💛 - Coveralls