Added password masking in Linux terminal

[srijondeb]

This pull request addresses Issue #97, which reports that passwords entered in the terminal are visible in plaintext when using 7-Zip with -p on Linux — a serious security concern.

While PR #33 also proposes a solution, this submission offers a slightly different approach by directly updating the GetPassword() function to perform platform-specific echo masking using termios on Linux.

Summary of Changes:

• Implements echo disabling using termios for Linux systems, mirroring existing Windows behavior via GetConsoleMode.
• Replaces std::endl (which causes compatibility issues with CStdOutStream) with '\n' followed by Flush() to prevent build-time errors.
• Ensures consistent password masking behavior across platforms.

Why This Matters:

This change ensures that password input on Linux no longer echoes to the terminal, reducing the risk of shoulder-surfing and inadvertent password leaks — improving both usability and security.

Fixes: #97