[foreign-jextract] RFR: 8257892: long double not handled by jextract [v6]

[Athijegannathan Sundararajan]

> added UnsupportedLayouts and checking/warning all unsupported types uniformly

Athijegannathan Sundararajan has updated the pull request incrementally with one additional commit since the last revision:

  FunctionDescriptor resultLayout checked for null explicitly

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Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/409/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/409/files/f2522cd5..2c250291

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=409&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=409&range=04-05

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/409.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/409/head:pull/409

PR: https://git.openjdk.java.net/panama-foreign/pull/409