* Add type adapters for `java.time` classes.

These adapters essentially freeze the JSON representation that
`ReflectiveTypeAdapterFactory` established by default, based on the
private fields of `java.time` classes. That's not a great
representation, but it is understandable. Changing it to anything else
would break compatibility with systems that are expecting the current
format.

If Gson had been updated with `java.time` adapters at the time the
`java.time` API was added, the representation would surely have been
something else, probably ISO standard formats. We can still supply
non-default adapters for that, but we'll still need to have these legacy
adapters by default.

I've been meaning to make this change for a while, but the need to do so
becomes more urgent with [this JDK
commit](openjdk/jdk@cc05530)
which makes a number of `java.time` fields `transient`. That means that
the reflective-based adapter will no longer work with the classes that
were changed.

* Apply a couple of Error Prone suggestions.

* Reformat a couple of source files.

* Fix another EP warning.

* Fix a particularly annoying EP warning/error.

* Update the Android API level.

I think it is time to do this, but obviously it should be a separate PR.

* Substantial rework.

* Move the new `TypeAdapter` implementations into a new class
  `JavaTimeTypeAdapters`. This allows us to omit that class from Android
  builds where it otherwise triggers warnings about SDK levels.

* Ensure that every `java.time` class that needs a `TypeAdapter` has
  one. This doesn't include "subpackages" `java.time.*` like
  `java.time.chrono`, where it doesn't appear that there are any classes
  that are likely to be serialized to JSON.

* Fix the handling of `ZoneId` and its subclasses.

* refactor: slightly optimize ConstructorConstructor (#2950)

* refactor: slightly optimize ConstructorConstructor

* Update comments

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* spotless apply

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

---------

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* Fix outdated comment (#2954)

* Compilation fixes.

I copied the internal version that was running on Google's
infrastructure, and some adjustments were needed.

* Fix lint errors.

* Fix a particularly annoying lint error.

* Fix the fix.

* Further fixes.

This still doesn't pass with a local build, and I may need to debug an
OSGi problem.

* Revert to Android API 23, but with gummy-bears-api.

* Annotate `JavaTimeTypeAdapters` to suppress animal-sniffer errors.

* Update `OSGiManifestIT` not to depend on order.

It appears that sometimes the clauses being checked for appear in the
other order, possibly because of a `HashMap` or the like somewhere in
the guts of OSGi. I haven't seen this on GitHub, but I do see it when
running locally with Google's JDK, which has more hash randomization.

* Fix use of assignment expression.

* Remove the parser, which was overkill.

It's enough just to swap the two clauses of a line when they are not in
the expected order.

Also, unrelatedly, update `protobuf-maven-plugin`.

* Use a local `@IgnoreJRERequirement`.

* Configure the local animal-sniffer annotation.

* Suppress IdentifierName warning.

* Update comments and undo an unnecessary split.

* Restore Math.toIntExact.

---------

Co-authored-by: 木葉 Scarlet <93977077+MukjepScarlet@users.noreply.github.com>
Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>