Add aliases for current_dir

[ear7h]

Aliases were added for the equivalent C/C++ APIs for POSIX and Windows. Also, I added one for pwd which users may be more familiar with, from the command line.

[rust-highfive]

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[rust-highfive]

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[thomcc]

According to https://std-dev-guide.rust-lang.org/documentation/doc-alias-policy.html this is fine:

We do expect that people might look for the Rust name of a function they reasonably expect to exist in Rust (e.g. a system function or a C library function), to try to figure out what Rust called that function.

@bors r+ rollup

[bors]

📌 Commit 84c80e7 has been approved by thomcc