Unify URI encoding/decoding, handle spaces-are-pluses, and handle hex/bin prefix automatically

[aaronfranke]

Made in response to #43929. The first two bullet points are one commit, the last three are the second commit.

• Make String::hex_to_int() and String::bin_to_int() automatically handle the prefix. This simplifies the code, both internally and for the end user. The p_with_prefix argument was not exposed in 3.2, so this doesn't break compat.

• Add BinToInt instance method to string in C#.

• Unify http_escape and percent_encode into uri_encode, and http_unescape and percent_decode into uri_decode.
  This restores part of Enhance uri utils #17583 and un-reverts that part's reversion Revert "Unify http- and percent- encode/decode" #18156 (see either of these for discussion).

• Tweak String::uri_decode() so that it handles spaces encoded as +.

• Add URIEncode and URIDecode instance methods to string in C#.

Me making this PR:

[akien-mga]

• Make String::hex_to_int() and String::bin_to_int() automatically handle the prefix. This simplifies the code, both internally and for the end user. The p_with_prefix argument was not exposed in 3.2, so this doesn't break compat.

From the code and docs, it seems like this does break compat as the argument was exposed. But I'm still OK with the change for 4.0.

[akien-mga]

• Make String::hex_to_int() and String::bin_to_int() automatically handle the prefix. This simplifies the code, both internally and for the end user. The p_with_prefix argument was not exposed in 3.2, so this doesn't break compat.

From the code and docs, it seems like this does break compat as the argument was exposed. But I'm still OK with the change for 4.0.

The original statement was correct, it's not exposed in 3.2 indeed. It was exposed in 4.0 with the Variant refactor, but it's fine to unexpose it.

[akien-mga]

Thanks!