Expand test cases for number notations

[bartveneman]

See https://developer.mozilla.org/en-US/docs/Web/CSS/number

[Valid numbers](https://developer.mozilla.org/en-US/docs/Web/CSS/number#valid_numbers)

12          A raw <integer> is also a <number>.
4.01        Positive fraction
-456.8      Negative fraction
0.0         Zero
+0.0        Zero, with a leading +
-0.0        Zero, with a leading -
.60         Fractional number without a leading zero
10e3        Scientific notation
-3.4e-2     Complicated scientific notation

[Invalid numbers](https://developer.mozilla.org/en-US/docs/Web/CSS/number#invalid_numbers)

12.         Decimal points must be followed by at least one digit.
+-12.2      Only one leading +/- is allowed.
12.1.1      Only one decimal point is allowed.