It's in need for variable weight

[TimurGerasimov250]

It needs a variable weight axis from 100 to 900

[apoorvpotnis]

Related: #67.

As of now, I'm aware of only one math font which provides so many weights: Pennstander Math. Kp Math provides light and semibold weights, along with regular and bold.

One important benefit of doing a variable weight Noto Sans Math font would be that it'll provide math fonts for the hugely popular Open Sans, so it's like killing two birds in one stone.

[simoncozens]

Also related: harfbuzz/boring-expansion-spec#136