Text: negative dynamic `numberOfLines` are left unclamped

[mfkrause]

Surfaced by the new parity fuzzer from #26.

RN's Text clamps a negative numberOfLines to 0 at runtime. Boost replicates this only when the value is a numeric literal at build time. A non-literal value (a variable reference, or a value arriving through a spread) is left untouched, so the native host receives the negative number, which is invalid.

Repro

const n = () => -1;
<Text numberOfLines={n()}>hello</Text>

• Expected: numberOfLines: 0
• Actual: numberOfLines: -1