[foreign-jextract] RFR: 8251044: JextractTool API refactoring parse/filter/generate/write static methods in the same tool main class

[Athijegannathan Sundararajan]

JextractTool class for simple jextract API.

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Commit messages:
 - Removed ConstantParser abstraction. Trailing whitespace removed in FunctionalInterfaceScanner.java
 - removing trailing whitespace in JextractTool.java
 - moved Options class and tool error messages resource to impl package.
 - JDK-8251044: JextractTool API refactoring parse/filter/generate/write static methods in the same tool main class

Changes: https://git.openjdk.java.net/panama-foreign/pull/276/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/276/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251044
  Stats: 3531 lines in 30 files changed: 1665 ins; 1831 del; 35 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/276.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/276/head:pull/276

PR: https://git.openjdk.java.net/panama-foreign/pull/276