Themes: Allow template loading functions to pass additional arguments to the template via the $args parameter.
This affects:
get_header()
get_footer()
get_sidebar()
get_template_part()
locate_template()
load_template()
Note: get_search_form() already passes additional arguments to the template as of [44956].
Props enrico.sorcinelli, sc0ttkclark, scribu, nacin, wonderboymusic, GeertDD, beatpanda, amaschas, mintindeed, ysalame, caiocrcosta, bigdawggi, julianm, eddiemoya, shawnz, sayedwp, shamai, mboynes, mihai2u, guidobras, Mte90, apedog, stuffradio, overclokk, johnbillion, joyously, afercia, audrasjb, justlevine, SergeyBiryukov.
See #21676.