Pilot Implementation of HIV Self-Testing Delivery in Private Pharmacies Combined With a Respondent-Driven Sampling Method to Improve HIV Testing for Men Who Have Sex With Men and Transgender Women in Phnom Penh (ANRS 0100s): Protocol for a Prospective Mixed Method Feasibility Study - Chhavarath Dary; Olivier Ségéral; Joseph Larmarange; Emilie Mosnier; Mohamed Ben Mechlia; Vichea Ouk; Bruno Spire; Vonthanak Saphonn (JMIR Research Protocols)