Reland "Rename ProxyChain and ProxyResolver Apple classes"

This reverts commit a7a7732586d82b8b2ca2bb5b5c0254d3f6eae9b6.

Reason for revert: Reverted https://chromium-review.googlesource.com/c/chromium/src/+/5190661.

Original change's description:
> Revert "Rename ProxyChain and ProxyResolver Apple classes"
>
> This reverts commit 782da25142cbbe236eafa5d216911072d34655f0.
>
> Reason for revert: Blocker for reverting https://chromium-review.googlesource.com/c/chromium/src/+/5190661
>
> Original change's description:
> > Rename ProxyChain and ProxyResolver Apple classes
> >
> > ProxyChain and ProxyResolver are used both by macOS and iOS, so this
> > follows the naming convention to change to something more suggestive.
> >
> > Bug: None
> > Change-Id: I1f6bb242d22e5fe57bc036d6504a6ddcca0e4164
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5198057
> > Reviewed-by: Adam Langley <agl@chromium.org>
> > Reviewed-by: Paul Jensen <pauljensen@chromium.org>
> > Commit-Queue: Tiago Vignatti <tvignatti@igalia.com>
> > Cr-Commit-Position: refs/heads/main@{#1247698}
>
> Bug: None
> Change-Id: Ie730f53e449617aec63c1983ee3f4692ba6b3e16
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5202120
> Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Owners-Override: Tsuyoshi Horo <horo@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1247868}

Bug: None
Change-Id: I4940dda287c5cfea6215152c6c5c1e9d8a8dab95
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5202538
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1248457}

• net/BUILD.gn[diff]
• net/proxy_resolution/configured_proxy_resolution_service.cc[diff]
• net/proxy_resolution/proxy_chain_util_apple.cc[Renamed from net/proxy_resolution/proxy_chain_util_mac.cc - diff]
• net/proxy_resolution/proxy_chain_util_apple.h[Renamed from net/proxy_resolution/proxy_chain_util_mac.h - diff]
• net/proxy_resolution/proxy_chain_util_apple_unittest.cc[Renamed from net/proxy_resolution/proxy_chain_util_mac_unittest.cc - diff]
• net/proxy_resolution/proxy_config_service_ios.cc[diff]
• net/proxy_resolution/proxy_config_service_mac.cc[diff]
• net/proxy_resolution/proxy_resolver_apple.cc[Renamed from net/proxy_resolution/proxy_resolver_mac.cc - diff]
• net/proxy_resolution/proxy_resolver_apple.h[Added - diff]
• net/proxy_resolution/proxy_resolver_mac.h[Deleted - diff]