Add base58_encode/decode functions

[nicolas-grekas]

Currently, the base58-encoding has to be implemented in PHP, which is slow compared to native code doing the same.

Base58 encoding produces strings that have desirable characteristics compared to base64:

• URL friendly (no /+ or -_ to deal with)
• less confusable characters (no 0Ilo)
• output of similar size (~73% vs 75%)

This makes it perfect to represent unique identifiers or hashes for example. symfony/uid implements it and my feeling is that it's getting increasingly popular.

Having a native and fast implementation would be nice.

See https://en.wikipedia.org/wiki/Binary-to-text_encoding#Base58 for some more background.

[remicollet]

Notice that https://pecl.php.net/package/base58 exists
This extensions requires https://github.com/luke-jr/libbase58

[cmb69]

Right, since there is already a PECL package, adding support for base58 encoding/decoding certainly would require the RFC process.

[github-actions]

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