[foreign-memaccess] RFR: JDK-8241866:Add API to reshape sequence layouts

[Maurizio Cimadamore]

https://docs.scipy.org/doc/numpy/reference/generated/numpy.reshape.html

As in Python, clients can use _at most_ one `-1` dimension value, and that dimension value will be inferred by
remaining dimensions.

The changes also add the `flatten` method, which does the opposite - e.g. take a sequence layout, whose element layout
could be other nested sequence layouts and flatten everything into an outermost sequence layout (where element count is
adjusted as needed).

These routines are fairly general and helpful and I found myself in need for something similar when writing code doing
parallel processing of memory segments, but there are many other possible use cases.

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Commit messages:
 - Fix whitespaces
 - Forgot to add file
 - Add SequenceLayout::reshape/flatten

Changes: https://git.openjdk.java.net/panama-foreign/pull/75/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/75/webrev.00
  Stats: 305 lines in 3 files changed: 304 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/75.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/75/head:pull/75

PR: https://git.openjdk.java.net/panama-foreign/pull/75