Expose more of std::path
Expose more of std::path

This commit exposes the `is_sep` function and `MAIN_SEP` constant, as
well as Windows path prefixes. The path prefix enum is safely exposed on
all platforms, but it only yielded as a component for Windows.

Exposing the prefix enum as part of prefix components involved changing
the type from `OsStr` to the `Prefix` enum, which is a:

[breaking-change]

rprichard/rust,aneeshusa/rust,mahkoh/rust,cllns/rust,zubron/rust,carols10cents/rust,KokaKiwi/rust,omasanori/rust,dwillmer/rust,jroesch/rust,zachwick/rust,sae-bom/rust,l0kod/rust,ebfull/rust,AerialX/rust-rt-minimal,vhbit/rust,cllns/rust,sae-bom/rust,graydon/rust,ebfull/rust,reem/rust,ejjeong/rust,AerialX/rust,victorvde/rust,dwillmer/rust,carols10cents/rust,omasanori/rust,miniupnp/rust,graydon/rust,l0kod/rust,nwin/rust,XMPPwocky/rust,sae-bom/rust,mahkoh/rust,pelmers/rust,jashank/rust,aneeshusa/rust,ejjeong/rust,ebfull/rust,sae-bom/rust,graydon/rust,robertg/rust,kwantam/rust,zaeleus/rust,ejjeong/rust,pshc/rust,vhbit/rust,rohitjoshi/rust,nwin/rust,aneeshusa/rust,AerialX/rust-rt-minimal,mihneadb/rust,jroesch/rust,philyoon/rust,andars/rust,philyoon/rust,AerialX/rust,dwillmer/rust,aneeshusa/rust,untitaker/rust,krzysz00/rust,pelmers/rust,mihneadb/rust,avdi/rust,jroesch/rust,jroesch/rust,mdinger/rust,pelmers/rust,TheNeikos/rust,jashank/rust,richo/rust,zachwick/rust,zachwick/rust,omasanori/rust,pshc/rust,nwin/rust,pshc/rust,mdinger/rust,zaeleus/rust,nwin/rust,KokaKiwi/rust,GBGamer/rust,kwantam/rust,ebfull/rust,AerialX/rust,miniupnp/rust,aneeshusa/rust,zubron/rust,rohitjoshi/rust,pelmers/rust,jashank/rust,andars/rust,richo/rust,richo/rust,KokaKiwi/rust,rohitjoshi/rust,mdinger/rust,jashank/rust,vhbit/rust,zubron/rust,victorvde/rust,jashank/rust,jashank/rust,zachwick/rust,robertg/rust,XMPPwocky/rust,AerialX/rust-rt-minimal,untitaker/rust,nwin/rust,aepsil0n/rust,richo/rust,untitaker/rust,jroesch/rust,l0kod/rust,ebfull/rust,ruud-v-a/rust,rohitjoshi/rust,aepsil0n/rust,rohitjoshi/rust,vhbit/rust,seanrivera/rust,cllns/rust,miniupnp/rust,aneeshusa/rust,krzysz00/rust,KokaKiwi/rust,seanrivera/rust,rprichard/rust,mahkoh/rust,krzysz00/rust,cllns/rust,XMPPwocky/rust,mvdnes/rust,cllns/rust,gifnksm/rust,andars/rust,robertg/rust,XMPPwocky/rust,mahkoh/rust,GBGamer/rust,omasanori/rust,AerialX/rust,carols10cents/rust,zubron/rust,l0kod/rust,ejjeong/rust,gifnksm/rust,rprichard/rust,ruud-v-a/rust,nwin/rust,zaeleus/rust,TheNeikos/rust,mihneadb/rust,aidancully/rust,kwantam/rust,aepsil0n/rust,mihneadb/rust,mvdnes/rust,gifnksm/rust,nwin/rust,GBGamer/rust,mahkoh/rust,mdinger/rust,zubron/rust,carols10cents/rust,AerialX/rust-rt-minimal,aidancully/rust,mvdnes/rust,l0kod/rust,krzysz00/rust,kwantam/rust,pshc/rust,avdi/rust,philyoon/rust,dwillmer/rust,aidancully/rust,victorvde/rust,philyoon/rust,zachwick/rust,vhbit/rust,robertg/rust,pelmers/rust,reem/rust,rprichard/rust,vhbit/rust,avdi/rust,krzysz00/rust,ejjeong/rust,mdinger/rust,reem/rust,jashank/rust,victorvde/rust,XMPPwocky/rust,zubron/rust,untitaker/rust,graydon/rust,avdi/rust,jroesch/rust,ebfull/rust,victorvde/rust,mahkoh/rust,seanrivera/rust,GBGamer/rust,mdinger/rust,vhbit/rust,robertg/rust,omasanori/rust,sae-bom/rust,gifnksm/rust,l0kod/rust,miniupnp/rust,seanrivera/rust,seanrivera/rust,kwantam/rust,sae-bom/rust,carols10cents/rust,KokaKiwi/rust,mvdnes/rust,aepsil0n/rust,rprichard/rust,GBGamer/rust,GBGamer/rust,cllns/rust,richo/rust,graydon/rust,l0kod/rust,victorvde/rust,seanrivera/rust,pshc/rust,dwillmer/rust,miniupnp/rust,miniupnp/rust,KokaKiwi/rust,vhbit/rust,andars/rust,zubron/rust,avdi/rust,TheNeikos/rust,AerialX/rust-rt-minimal,mvdnes/rust,carols10cents/rust,reem/rust,philyoon/rust,zaeleus/rust,omasanori/rust,TheNeikos/rust,GBGamer/rust,aidancully/rust,pelmers/rust,miniupnp/rust,AerialX/rust,AerialX/rust,mihneadb/rust,rohitjoshi/rust,aidancully/rust,AerialX/rust-rt-minimal,untitaker/rust,miniupnp/rust,zaeleus/rust,graydon/rust,l0kod/rust,untitaker/rust,reem/rust,mihneadb/rust,reem/rust,aepsil0n/rust,GBGamer/rust,zaeleus/rust,jroesch/rust,zachwick/rust,ruud-v-a/rust,pshc/rust,gifnksm/rust,aepsil0n/rust,mvdnes/rust,dwillmer/rust,krzysz00/rust,gifnksm/rust,ruud-v-a/rust,ejjeong/rust,dwillmer/rust,ruud-v-a/rust,jroesch/rust,TheNeikos/rust,TheNeikos/rust,richo/rust,XMPPwocky/rust,avdi/rust,robertg/rust,pshc/rust,zubron/rust,philyoon/rust,dwillmer/rust,rprichard/rust,jashank/rust,nwin/rust,pshc/rust,andars/rust,kwantam/rust,ruud-v-a/rust,aidancully/rust,andars/rust