Core: Simulate write-only file access with read-write access (#3360)

* Swap write access mode for read write

Opening with access mode w will erase the opened file. We do not want this.

* Create mode

Opening with write access was previously the only way to create a file through open, so add a separate FileAccessMode that uses the write access mode to create files.

* Update file_system.cpp

Remove a hack added to posix_rename to bypass the file clearing behaviors of FileAccessMode::Write

* Check access mode in read functions

Write-only files cause the EBADF return on the various read functions. Now that we're opening files differently, properly handling this is necessary.

* Separate appends into proper modes

Fixes a potential regression from one of my prior PRs, and ensures the Write | Append flag combo also behaves properly in read-related functions.

* Move IsWriteOnly check after device/socket reads

file->f is only valid for files, so checking this before checking for sockets/devices will cause access violations.

* Fix issues

Now that Write is identical to ReadWrite, internal uses of Write need to be swapped to my new Create mode

* Fix remaining uses of FileAccessMode write to create files

Missed these before.

* Fix rebase

* Add stubbed get_authinfo (#3722)

* mostly stubbed get_authinfo

* Return value observed on console if get_authinfo was called for the current thread, esrch otherwise

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Co-authored-by: kalaposfos13 <153381648+kalaposfos13@users.noreply.github.com>
Co-authored-by: georgemoralis <giorgosmrls@gmail.com>

src/common/logging/backend.cpp

@@ -62,7 +62,7 @@ private:
 class FileBackend {
 public:
     explicit FileBackend(const std::filesystem::path& filename, bool should_append = false)
-        : file{filename, should_append ? FS::FileAccessMode::Append : FS::FileAccessMode::Write,
+        : file{filename, should_append ? FS::FileAccessMode::Append : FS::FileAccessMode::Create,
                FS::FileType::TextFile} {}
 
     ~FileBackend() = default;