Merge pull request grpc#18867 from lidizheng/backport-gevent-fix

Backport c-ares gevent segfault fix to v1.20.1

Merge pull request grpc#18760 from lidizheng/v1.20.x

Bump version to v1.20.0

Merge pull request grpc#18676 from lidizheng/v1.20.x

Bump version to v1.20.0-pre3

Merge pull request grpc#18640 from lidizheng/v1.20.x

Bump version to v1.20.0-pre2

Merge pull request grpc#18595 from lidizheng/v1.20.x

Update g_stands_for.md for v1.20.x

Merge pull request grpc#18301 from srini100/v1.19.x

V1.19.x

Merge pull request grpc#18166 from muxi/bump-protocompiler

ObjC v1.19.0 batch patch

Merge pull request grpc#18035 from srini100/v1.19.x

Bump version to pre1

Merge pull request grpc#17712 from sanjaypujare/releasing-v1.18.x

Releasing v1.18.x

Merge pull request grpc#17627 from sanjaypujare/releasing-v1.18.x

Change the version suffix from dev to pre1 and regenerate projects