Fixes commas (if per-player-locale) is enabled else uses NumberUtils default Locale for /pay

[Kyriakum]

• Added locale functionality to /pay command
• Added tests for String to BigDecimal parsing & locale specific parsing

Information

This PR fixes #2355 .

Details

Proposed fix:

NumberUtils.java includes PRETTY_LOCALE which uses as default for PRETTY_FORMAT
NumberUtils.java includes 2 new methods for parsing Strings to BigDecimals in default locale OR specified locale.
Commandpay.java uses those two new methods to parse the String to BigDecimal according to whether per-player-locale is enabled or not
/pay String to BigDecimal parsing moved from Commandpay.java to NumberUtils.java
Instead of parsing manually with regex, use NumberFormat instead to make sure parsing is done as intended
Regex filtering & empty string checking is still left in Commandpay.java to handle wrong inputs from the user

Environments tested:

OS: Windows 11

Java version: java version "21.0.4" 2024-07-16 LTS

• Most recent Paper version (1.XX.Y, git-Paper-BUILD)
• CraftBukkit/Spigot/Paper 1.12.2
• CraftBukkit 1.8.8
• Paper 1.19.4

Demonstration: