rdp: convert to JsonBuilder, and use applayer incomplete

[lmzke]

Make sure these boxes are signed before submitting your Pull Request -- thank you.

• I have read the contributing guide lines at https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Contributing
• I have signed the Open Information Security Foundation contribution agreement at https://suricata-ids.org/about/contribution-agreement/
• I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Link to redmine ticket:

• https://redmine.openinfosecfoundation.org/issues/3539
• https://redmine.openinfosecfoundation.org/issues/3715

Resolves two issues earmarked for 6.0.0rc1:

• rdp: remove parser buffering code (for 3539)
• rdp/eve: convert to jsonbuilder (for 3715)

In addition to CI, cargo test and suricata-verify both pass as well.

Feedback welcome.

[victorjulien]

Thanks Zach, could you please split the commits that do functional changes from the commits that do reformatting?

[lmzke]

Continued in #5199.