gRPC-Core Release 1.25.0

[Yash Tibrewal]

This is the v1.25.0 (game) release announcement for gRPC-Core and the wrapped languages C++, C#, Objective-C, Python, PHP and Ruby. Latest release notes are here.

This release contains refinements, improvements, and bug fixes, with highlights listed below.

Core

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-  Change RR to consider a subchannel in TF if it has failed since it was READY. ([#20245](https://github.com/grpc/grpc/pull/20245))

-  Fix a use after free in c-ares on Windows. ([#20274](https://github.com/grpc/grpc/pull/20274))

C++

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-  Honor CARES_ROOT_DIR. ([#20630](https://github.com/grpc/grpc/pull/20630))

-  make cmake grpc.pc depend on openssl too. ([#20621](https://github.com/grpc/grpc/pull/20621))

-  Create pkg-config files from CMake. ([#20211](https://github.com/grpc/grpc/pull/20211))

-  Add C++ wrapper for SPIFFE credentials v2. ([#19778](https://github.com/grpc/grpc/pull/19778))

-  Upgrade bazel to 0.29.1. ([#20222](https://github.com/grpc/grpc/pull/20222))

C#

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-  Provide length when getting serialization buffer writer. ([#20691](https://github.com/grpc/grpc/pull/20691))

-  Fix error when changing Protobuf item values in Visual Studio. ([#20569](https://github.com/grpc/grpc/pull/20569))

-  Add generic variance to reader and writer interfaces. ([#20549](https://github.com/grpc/grpc/pull/20549))

Objective-C

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-  Added convenience class GRPCUnaryResponseHandler for unary calls. ([#20560](https://github.com/grpc/grpc/pull/20560))

-  Fixed an issue where Swift application depending on gRPC is unable to archive. ([#20527](https://github.com/grpc/grpc/pull/20527))

PHP

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-  PHP: fix zend_hash_str_del() segfault. ([#20249](https://github.com/grpc/grpc/pull/20249))

Python

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-  Add experimental option to run unary-stream RPCs on a single Python thread. ([#20753](https://github.com/grpc/grpc/pull/20753))

-  [AIO] Minimal AsyncIO Server. ([#20598](https://github.com/grpc/grpc/pull/20598))

-  Switch to concrete classes in experimental asyncio. ([#20326](https://github.com/grpc/grpc/pull/20326))

-  Add manylinux2010_x86 wheels into artifacts. ([#20673](https://github.com/grpc/grpc/pull/20673))

-  Release 3.8 binary wheels. ([#20616](https://github.com/grpc/grpc/pull/20616))

-  Make grpc_testing's Servicer context abort method stop execution of the servicer handler. ([#20426](https://github.com/grpc/grpc/pull/20426))

-  Build Python wheels with tag manylinux2010. ([#20282](https://github.com/grpc/grpc/pull/20282))

-  Add experimental support for asyncio unary client. ([#19960](https://github.com/grpc/grpc/pull/19960))