Bring back script encryption in export preset

[Xrayez]

What started as curiosity ended up as an actual implementation. 😁

Retrieved working implementation from 2.1 branch and adapted to
existing export preset system.

Added Script tab in export preset to export script as raw text,
compiled, or encrypted (same as in 2.1). The script encryption key is
visually validated. The script export mode and the key is saved per
per preset in `export_presets.cfg`, so it makes sense to ignore this
file in version control system.

Each custom exporting procedure can retrieve an export preset set
during project exporting. Refactored project export dialog a bit to
allow easier code comprehension.

Tested in both debug and release modes, with text, compiled, and encrypted modes respectively. If wrong key is provided during export, the exported project will crash, which is expected:

ERROR: open_and_parse: Condition ' String::md5(md5.digest) != String::md5(md5d) ' is true. returned: ERR_FILE_CORRUPT
      At: core/io/file_access_encrypted.cpp:103

The scripts are exported as .gde as before. The default script export mode is still Compiled, not Text.

I'll also write documentation for this in godot-docs.

Fixes #24121.

Also, Merry Christmas! 🎄

[girng]

wow... glad it's back thank you

[Xrayez]

As been discussed in linked issues, perhaps we should rename script export mode from Compiled to Binary to avoid confusion, and leave Compiled for an actual implementation.

[akien-mga]

Thanks!