Previously, the testScaleUp() test was taking too much resources and
causing test resources to be terminated before the test could finish.
This commit lowers the intensity of the test, while still retaining the
verified behaviour (i.e., when restoring the Kafka consumer with higher
parallelism and more Kafka partitions).

This closes #5201.

This closes #5193.

[FLINK-8268][streaming][tests] Improve TwoPhaseCommitSinkFunctionTest stability by using custom in memory storage

The previous link was referencing a non-existent constructor signature.

FlinkKafkaProducer010Configuration is the return type of the deprecated
writeToKafkaWithTimestamp factory methods. Therefore, the class should
also be deprecated as well.

This commit moves deprecated factory methods of the
FlinkKafkaProducer010 behind regular constructors, for better navigation
and readability of the code.

This closes #5179.

This closes #5121.

This makes it easier for users and contributors to figure out how
to create local file paths in way that works cross operating systems.

The input stream from ByteStreamStateHandle did not overwrite the 'read(byte[], int, int)' method,
meaning that bulk byte reads resulted in many individual byte accesses.

Additionally, this change avoids accessing the data array through an outer class, but instead adds
a reference directly to the input stream class, avoiding one hop per access. That also allows
a more restricted access level on the fields, which may additionally help the jitter in some cases.

Previously, this converted Flink paths (internally URIs) to strings and
then let the Hadoop Paths parse, validate, and normalize the strings to
URIs again.

Now we simply pass the URIs directly.

This avoids going though an exception in the case of non-existing files.

The fact that the method was never called (and never implemented) strongly suggests
that it should be removed, otherwise someone might eventually end up implementing
it for a new state backend and wonder why it is never called.

[FLINK-8373] [core, hdfs] Ensure consistent semantics of FileSystem.mkdirs() across file system implementations.

This closes #5231

This closes #5204

This closes #5178

This closes #5238

Fix typos from the IntelliJ "Typos" inspection.

This closes #5242

This closes #5237

[FLINK-8203] [FLINK-7681] [table] Make schema definition of DataStream/DataSet to Table conversion more flexible

This closes #5132.

This closes #5065.

This closes #5218

Previously, NettyBufferPool only wrapped PooledByteBufAllocator but then, any
allocated buffer's alloc() method was returning the wrapped
PooledByteBufAllocator which allowed heap buffers again. By extending the
PooledByteBufAllocator, we prevent this loop hole.

This also fixes the invariant that a copy of a buffer should have the same
allocator.

This closes #4594.