Update CHANGES.txt for 3.10.1 release

Ported names fix for Ruby to the release branch

Update protobuf version to 3.10.1

Backport #6759 and disable extension code gen for C#

Update CHANGES.txt with changes since 3.10.0-RC1

* Initialize well known type values

Also fixes #6667

* Revert unwanted change

The new function name also better reflects the semantics of the
function.  Like timegm(), this function always converts to/from
UTC, not local time.

Pull the ObjC fixes from #6679 to the 3.10.x branch

The OSReadLittleInt64 function as defined by Apple reduces down to:

`return *(volatile uint64_t *)((uintptr_t)base + byteOffset);`

which means we are type-punning using a cast. On ARMv7 and other aligned architectures this can cause crashes. 
Minimal example: https://gist.github.com/dmaclach/b10b0a71ae614d304c067cb9bd264336

Fixes #6679 

The code in question hasn't change in a long time so the cause of
https://github.com/firebase/firebase-ios-sdk/issues/3851 still appears to be
an Xcode 11 clang change/bug; but this does appear to be slightly better
code for the work being done.

Cleanup along the way for #6679 

Update protobuf version to 3.10.0 stable

Fix update_version.py, so that PROTOBUF_VERSION is always a 9 digit number

Update protobuf version for Java and PHP

Cherry Pick (#6614)

* Sync upb

https://github.com/protocolbuffers/upb/pull/209

* Update upb

https://github.com/protocolbuffers/upb/pull/210

Java: Add Automatic-Module-Name entries to the Manifest

This commit removes the question template. It also updates the bug report and feature request templates to direct questions to the mailing list.

* When length is zero, substr returns null instead of emptry string, which breaks the invariable for message.
* Tested in https://github.com/protocolbuffers/protobuf/pull/6560

Update version number

* For missing message value, map should create a default message
instance in order to keep its invariable.
* On 32-bit platform, int64 map key should be string