Enable Fast Floating-Point reading/writing by default in 3.0

[cowtowncoder]

For Jackson 2.x we have following features disabled by default:

• StreamReadFeature.USE_FAST_DOUBLE_PARSER
• StreamReadFeature.USE_FAST_BIG_NUMBER_PARSER
• StreamWriteFeature.USE_FAST_DOUBLE_WRITER

that is, for FP reading to use default JDK implementation and not one from FastDoubleParser (read) / Schubfach (write). This to minimize any chance of breakage, to require users to opt-in for optimized handling.

Since there hasn't been reports of issues during the time we've had (since 2.14, more than a year), it seems reasonable to assume things work well: so let's enable "fast FP" handling by default for 3.0.
We can still consider similar change for later 2.x, but let's start with 3.0.