RFR: 7903983: Remove redundant findOrThrow method

[Nizar Benalla]

`SymbolLookup::FindOrThrow` was introduced in JDK 23, making this method in the generated code redundant:

  static MemorySegment findOrThrow(String symbol) {
      return SYMBOL_LOOKUP.findOrThrow(symbol);
  }

The generated method should have been dropped in https://github.com/openjdk/jextract/commit/a53f5c05e3ee2cca057cadb78b2e381c39f943d7 but I didn't cleanup all uses of it.

A small additional cleanup in PR is that the newly added option for framworks now uses `--` rather than `-`

TIA

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Commit messages:
 - remove rendundant method
 - longer cmd option should use -- rather than -

Changes: https://git.openjdk.org/jextract/pull/280/files
  Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=280&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903983
  Stats: 27 lines in 5 files changed: 3 ins; 4 del; 20 mod
  Patch: https://git.openjdk.org/jextract/pull/280.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/280/head:pull/280

PR: https://git.openjdk.org/jextract/pull/280