RFR: 8358540: Enhance MathUtils in view of FloatingDecimal enhancements

[Raffaello Giulietti]

On Wed, 4 Jun 2025 14:22:43 GMT, Raffaello Giulietti <rgiulietti at openjdk.org> wrote:

> Another step in enhancing floating-point <-> decimal conversions.

Changes include, but are not limited to:
- Accessing `g0()` and `g1()` with the exponent rather than the negated exponent.
- Inverting the order of the `MathUtils.g` table.
- Expanding the `MathUtils.g` table with more entries.
- Expanding the `MathUtils.pow10` table with more entries.
- Enhanced and simplified tests.
- Overall better documentation.

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PR Comment: https://git.openjdk.org/jdk/pull/25641#issuecomment-2940269391