[foreign-jextract] RFR: 8246611: jextract generated allocate methods should accept CScope and callback allocate should auto-register

[Athijegannathan Sundararajan]

* moved CScope out of RuntimeHelper
* Cint, Cfloat, callback allocate overloads accept CScope
* callback allocate overload that accept CScope registers callback with it

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Commit messages:
 - 8246611: jextract generated allocate methods should accept CScope and callback allocate should auto-register
 - sqlite3_free should not be commented. Fixed free of wrong pointer.
 - adding sqlite3 sample

Changes: https://git.openjdk.java.net/panama-foreign/pull/195/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/195/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8246611
  Stats: 369 lines in 13 files changed: 302 ins; 51 del; 16 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/195.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/195/head:pull/195

PR: https://git.openjdk.java.net/panama-foreign/pull/195