[skip ci]

Change-Id: I1ba6f6372a08b5796570851336e1a548602f60da

[skip ci]

Change-Id: I1ba6f6372a08b5796570851336e1a548602f60da

Also pull the watchos support info from master.

As bazel folks are looking at getting auto generation of module maps going and
the importing of sources files causes issues there.  We were only do it to
hack around some of the apple linker behaviors around objc classes and
categories, but even that isn't complete and CocoaPods was already doing -ObjC,
and developers not using pods could have still needed it to ensure everything
was linked anyways; so drop the hack of importing sources.

- Add generator constant for the default framework name.
- Add generator api for making the CPP symbol from the name.
- Add generator api to see if it is a bundled proto file.
- Output a CPP conditional and two imports for the core library headers.
- Add helper for generating the #import for file headers to deal with the
  framework imports.
- Add a reference from the unittests to a WKT to use that to inspect how
  imports generate.
- Update the podspec to define the CPP symbol and require pods 1.0 (or later).

Fixes https://github.com/google/protobuf/issues/1457

NOTE: This is a binary breaking change as structure sizes have changed size
and/or order.

- Drop capturing field options, no other options were captured and other mobile
  targeted languages don't try to capture this sort information (saved 8
  bytes for every field defined (in static data and again in field descriptor
  instance size data).
- No longer generate/compile in the messages/enums in descriptor.proto. If
  developers need it, they should generate it and compile it in. Reduced the
  overhead of the core library.
- Compute the number of has_bits actually needs to avoid over reserving.
- Let the boolean single fields store via a has_bit to avoid storage, makes
  the common cases of the instance size smaller.
- Reorder some flags and down size the enums to contain the bits needed.
- Reorder the items in the structures to manually ensure they are are packed
  better (especially when generating 64bit code - 8 bytes for every field,
  16 bytes for every extension, instance sizes 8 bytes also).
- Split off the structure initialization so when the default is zero, the
  generated static storage doesn't need to reserve the space. This is batched
  at the message level, so all the fields for the message have to have zero
  defaults to get the saves. By definition all proto3 syntax  files fall into
  this case but it also saves space for the proto2 that use the standard
  defaults. (saves 8 bytes of static data for every field that had a zero
  default)
- Don't track the enums defined by a message. Nothing in the runtime needs it
  and it was just generation and runtime overhead. (saves 8 bytes per enum)
- Ensure EnumDescriptors are started up threadsafe in all cases.
- Split some of the Descriptor initialization into multiple methods so the
  generated code isn't padded with lots of zero/nil args.
- Change how oneof info is feed to the runtime enabling us to generate less
  static data (8 bytes saved per oneof for 64bit).
- Change how enum value informat is capture to pack the data and only decode
  it if it ends up being needed. Avoids padding issues causing bloat of 64bit,
  and removes the needs for extra pointers in addition to the data (just the
  data and one pointer now).

The new version of Cocoapods requires it even when using the podspec locally.

It's already submitted.

This was released as `3.0.0-alpha-4.1`

Protoc, C++ runtime and Java runtime are updated to v3.0.0-beta-1, other
languages are updated to v3.0.0-alpha-4.

Also add WKT headers to the umbrella file, and simplify Podspec with it.
Plus some layout improvements to the BUILD file.

Apparently, in Cocoapods, all recursive #imports of public headers need
to be public.