Refactor a number of methods in `PDFViewerApplication` to be `async` rather than manually returning `Promise`s
Refactor a number of methods in `PDFViewerApplication` to be `async` rather than manually returning `Promise`s

*Ignoring whitespace changes is probably necessary, in order for the diff to be readable.*

timvandermeij/pdf.js,timvandermeij/pdf.js,xavier114fch/pdf.js,macroplant/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,caremerge/pdf.js,Snuffleupagus/pdf.js,mainegreen/pdf.js,Shoobx/pdf.js,showpad/mozilla-pdf.js,Snuffleupagus/pdf.js,mozilla/pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,xavier114fch/pdf.js,timvandermeij/pdf.js,macroplant/pdf.js,mozilla/pdf.js,caremerge/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,mukulmishra18/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,mainegreen/pdf.js,Shoobx/pdf.js,nawawi/pdf.js,mukulmishra18/pdf.js