[foreign-memaccess+abi] RFR: 8292918: Split FunctionDescriptor into an interface and implementation(s) [v2]

[Per Minborg]

> This PR splits the current FunctionDescription class into an interface and two internal implementing classes.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Relax parameter checking

-------------

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/713/files
  - new: https://git.openjdk.org/panama-foreign/pull/713/files/6cfea9f6..e870fb55

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=713&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=713&range=00-01

  Stats: 12 lines in 1 file changed: 1 ins; 10 del; 1 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/713.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/713/head:pull/713

PR: https://git.openjdk.org/panama-foreign/pull/713