* Fix #5513

* Added tests for invalid lengths when reading strings and bytes.
Added test for reading tags with invalid wire types in unknown field set.
Changed invalid length check in ReadString to match the one in ReadBytes

Signed-off-by: Xiang Dai <764524258@qq.com>

* Modify how end tags are encounted in merge code (compiler)

* Modify how end tags are encounted in merge code (generated)

* Modify how end tags are encounted in merge code (library)

* Regenerate generated code through generate_descriptor_proto.sh

* Down-integrate internal changes to github.

* Fix BUILD file and regenerate csharp descritpor

* Down-integrate internal changes to github.

* fix csharp conformance test

* add comments in conformance.proto for text format

* fix comments

* fix comments, re-generated csharp file

* fix comments, re-generated csharp file

Even though the comments were indented to appear to go with the jspb
case/field, protoc doesn't collect comments like that, so these "hanging"
comments actually "attach" to the next thing added to each.  Looking at
https://github.com/protocolbuffers/protobuf/pull/5566 you see where
the generated code picked up the comment on the wrong field.

* Down-integrate internal changes to github.

* fix python conformance test

* fix csharp conformance test

* add back java map_lite_test.proto's optimize for option

* fix php conformance test

* Down-integrate internal changes

* Update generated code for php, objc and csharp.

* Add missing dependency in conformance_php

Replace update_version shell script with a python script, which is much better at handling XML rewrite. Update the PHP version too. As part of rewrite, some XML file format will change a little, but the semantics is still the same so it should be okay.

Fix TimestampPartial operator == overload implementation: Cannot call == inside it, otherwise it would cause stack overflow

* Increase C# default recursion limit to 100

This matches the Java and C++ defaults.

* Change compatibility tests to use execution-time default recursion limit

This way the same tests should pass against all versions, even
if the recursion limit changes. (The tests will be testing whether
different messages work, admittedly - but that's probably fine.)

Add group support for proto2

* Ported FieldMaskUtil from Java to C#

* Merged FieldMaskUtil into FieldMaskPartial

- Removed FieldMaskUtil
- Moved FieldMaskTree to root
- Updated tests

* Improved tests

- Removed internal method FieldMaskTree.GetFieldPaths
- Proof FieldMask.Paths only contains expected values

* Added FieldMaskTreeTest to Makefile

* Added FieldMaskTree to Makefile

* Compiler changes

* Generated code changes

* Library changes

* Compiler style changes

* Generated style changes

* Fix Windows build errors

* Implement changes from review

* Reintroduce proto2 check

* Compiler changes (required handling review)

* Generated code changes (required handling review)

* Library changes (required handling review

* Field presence rewrite (compiler changes)

* Field presence rewrite (generated code changes)

* Compiler comment

* IFieldAccessor.HasValue library implementation

* Remove Clear methods and default values from proto3 code (Compiler)

* Remove Clear methods and default values from proto3 code (Generated)

* Remove Clear methods and default values from proto3 code (Library)

* Fix distcheck error

* Rewrite default string values to use base64 and convert

* Library changes (IMessage2)

* Compiler changes (IMessage2)

* Generated changes (IMessage2)

* Rebased and regenerated

* Compiler changes (initialized extension)

* Generated changes (initialized extension)

* Library changes (initialized extension)

* Refactor MessageExtensions.IsRequired

* Move string default value creator and bytes default value creator back to seperate methods

* Dead code cleanup

* Fixed segmentation fault
Removed unused header method declarations

Rather than converting the proto to a ByteString again, use the
existing SerializedData property.

This is primarily for access to comments, which would be expected to be available in a protoc plugin.

The implementation has two fiddly aspects:

- We use a Lazy<T> to avoid building the map before cross-linking. An alternative would be to crosslink at the end of the constructor, and remove the calls to CrossLink elsewhere. This would be generally better IMO, but deviate from the Java code.
- The casts to IReadOnlyList<DescriptorBase> are unfortunate. They'll always work, because these lists are always ReadOnlyCollection<T> for a descriptor type... but we can't use IList<DescriptorBase> as that's not covariant, and it's annoyingly fiddly to change the field to be of type ReadOnlyCollection<T>.

This performs more testing for field descriptors built from byte
strings too, but that's mostly incidental. The chief intent is to
check that cross-linking occurs.

Related to #658 and #5007.

* Give a unique category to each test.

This change introduce a TestCategory enum to ConformanceRequest. Existing tests
are divided into three categories: binary format test, json format test and json
format (ignore unknown when parsing) test. For the previous two categories, there
is no change to existing testee programs. For tests with the last category, testee programs
should either enable ignoring unknown field during json parsing or skip the test.

* Fix python test

* Fix java

* Fix csharp

* Update document

* Update csharp generated code

* Enable ignoring unknown in json parsing in php

* Update generated descriptor files

* Update failure list for other languages.

* Remove unnecessary php files

This potentially avoids compiler warnings.