std.os.windows.advapi32: add RegOpenKeyExA and RegQueryValueExA

[FnControlOption]

Noticed these were missing while starting work on #6363. Might find more bindings to add in the coming days/weeks...

Question: RegOpenKeyExW is duplicated in std.os.windows.kernel32, so should it be deleted there, or should RegOpenKeyExA be added? (The C prototypes in winreg.h have WINADVAPI, so advapi32 is probably the better place for these over kernel32)

[squeek502]

W suffixed functions should always be preferred over A suffixed functions, and Zig's standard library is not intending on providing complete bindings, so I believe this PR is likely going to be rejected. From #4426 (comment):

This means removing the Windows extern functions that end in "A" is fair game now.

Relevant issues:

• switch to using 'W' versions of windows functions instead of 'A' #534
• reduce windows API bindings in the standard library to the minimum required for the standard library's own abstractions to work #4426
• Remove Windows *A declarations #9054

Part of the port of windows_sdk.cpp should be converting those A suffixed function calls to their W suffixed equivalents.

[FnControlOption]

Oops, thanks for clarifying. Dumb question, what is the standard way to create a wide string in Zig?

[squeek502]

what is the standard way to create a wide string in Zig?

Depends what you mean. If you want a UTF-16 string literal, you can use std.unicode.utf8ToUtf16LeStringLiteral. If you have a runtime string and need to get a wide string from it, there's std.unicode.utf8ToUtf16LeWithNull. If you're dealing with paths, there's things like std.os.windows.sliceToPrefixedFileW.