gui: explicitly disable "Dark Mode" appearance on macOS
gui: explicitly disable "Dark Mode" appearance on macOS

Github-Pull: #14593
Rebased-From: cf2f4306fe26305b24bba8833af845ada3a42ec8

GroestlCoin/GroestlCoin,vertcoin/vertcoin,lbryio/lbrycrd,h4x3rotab/BTCGPU,vmp32k/litecoin,thrasher-/litecoin,digibyte/digibyte,gjhiggins/vcoincore,lbryio/lbrycrd,h4x3rotab/BTCGPU,GroestlCoin/GroestlCoin,ahmedbodi/vertcoin,gjhiggins/vcoincore,GroestlCoin/bitcoin,BTCGPU/BTCGPU,guncoin/guncoin,thrasher-/litecoin,digibyte/digibyte,GroestlCoin/GroestlCoin,gjhiggins/vcoincore,lbryio/lbrycrd,gjhiggins/vcoincore,h4x3rotab/BTCGPU,vertcoin/vertcoin,thrasher-/litecoin,GroestlCoin/bitcoin,vmp32k/litecoin,GroestlCoin/GroestlCoin,GroestlCoin/bitcoin,qtumproject/qtum,gjhiggins/vcoincore,BTCGPU/BTCGPU,qtumproject/qtum,vmp32k/litecoin,lbryio/lbrycrd,h4x3rotab/BTCGPU,ahmedbodi/vertcoin,thrasher-/litecoin,BTCGPU/BTCGPU,vmp32k/litecoin,GroestlCoin/bitcoin,vmp32k/litecoin,vertcoin/vertcoin,digibyte/digibyte,ahmedbodi/vertcoin,vmp32k/litecoin,qtumproject/qtum,ahmedbodi/vertcoin,digibyte/digibyte,lbryio/lbrycrd,guncoin/guncoin,vertcoin/vertcoin,gjhiggins/vcoincore,BTCGPU/BTCGPU,vertcoin/vertcoin,digibyte/digibyte,lbryio/lbrycrd,thrasher-/litecoin,h4x3rotab/BTCGPU,digibyte/digibyte,guncoin/guncoin,ahmedbodi/vertcoin,guncoin/guncoin,BTCGPU/BTCGPU,qtumproject/qtum,thrasher-/litecoin,qtumproject/qtum,ahmedbodi/vertcoin,GroestlCoin/GroestlCoin,qtumproject/qtum,vertcoin/vertcoin,h4x3rotab/BTCGPU,GroestlCoin/GroestlCoin,qtumproject/qtum,BTCGPU/BTCGPU,GroestlCoin/bitcoin,guncoin/guncoin,lbryio/lbrycrd,GroestlCoin/bitcoin,guncoin/guncoin