Cherry-pick "Refactor Regexp.prototype"

Original change: https://chromium-review.googlesource.com/c/v8/v8/+/1547660
Adds unit test.

Bug: 147664838
Test: m -j proxy_resolver_v8_unittest && adb sync && adb shell \
      /data/nativetest/proxy_resolver_v8_unittest/proxy_resolver_v8_unittest
Merged-In: I6b8f8f2eff548cab5bbc69f7ba981381043227da
Change-Id: I6b8f8f2eff548cab5bbc69f7ba981381043227da
(cherry picked from commit 780b5e342028c8c7964145483ac73eca941ed464)