[Swift] Add -debug-prefix-map to map source file

[qyang-nj]

We use remote cache to speed up local builds. Because of this, we need to map server path to local path to enable local debugging.

settings set target.source-map "/server/path/repo" "/local/path/repo"

However, this stops working in Xcode 13. To make debugger work again, we need to

# during building
swiftc ... -debug-prefix-map /server/path/repo=.

# before debugging 
settings set target.source-map "." "/local/path/repo"

Please review

@xianwen @shepting

[xianwen]

Nice! Great work Qing!