Improve --remap-path-prefix documentation

[Urgau]

This PR improves the --remap-path-prefix documentation by:

• moving it into it's own page
• adding a small example
• mentioning that the remapping is best effort¹
• mentioning link.exe/PDB issues²
• mentioning the path separator issue (textual replacement)

r? @wesleywiser

Footnotes

1. #t-compiler > link.exe leaking paths in Windows PDB @ 💬 ↩

2. #t-compiler > link.exe leaking paths in Windows PDB @ 💬 ↩