[foreign-memaccess+abi] RFR: 8307253: Make FunctionDescriptor::toMethodType an instance method of Linker [v3]

[Maurizio Cimadamore]

> This patch moves `FunctionDescriptor::toMethodType` as an instance method of `Linker`. This allows linker implementations to be more opinionated on how the function descriptor -> method type conversion should behave.

Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Address review comments (check for padding during function descriptor construction)
 - Merge branch 'foreign-memaccess+abi' into toMethodType
 - Revert changes.
   Fix javadoc and impl for FunctionDescriptor::toMethodType to allow sequence layouts.
 - Initial push

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Changes: https://git.openjdk.org/panama-foreign/pull/830/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=830&range=02
  Stats: 75 lines in 5 files changed: 54 ins; 10 del; 11 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/830.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/830/head:pull/830

PR: https://git.openjdk.org/panama-foreign/pull/830