[SFrame-V3] libsframe: testsuite: add new testcases for SFRAME_FDE_TYPE_FLEX

[SFrame-V3] libsframe: testsuite: add new testcases for SFRAME_FDE_TYPE_FLEX

This patch adds two new tests for SFrame V3 changes, focusing on the
newly added flexible FDE TYPE SFRAME_FDE_TYPE_FLEX.

Following tests are added:
  - be-flipping-v3.c: Validates that big-endian SFrame V3 data is
    correctly endian flipped when run on little-endian hosts.  It
    verifies the decoding of CFA offsets and the new V3 register/offset
    metadata bitfields using the SFRAME_V3_FLEX_FDE_OFFSET_REG_* macros.
  - findfre-flex-1.c: Tests a variety of sframe_find_fre lookup
    scenarios, apart from checking the basic encoder/decoder APIs.

Documentation for the binary test data DATA-BE-V3 is provided in
README-be-flipping-v3 to ensure reproducibility.

libsframe/
	* Makefile.in: Regenerate.
	* testsuite/libsframe.decode/DATA-BE-V3: New test data.
	* testsuite/libsframe.decode/README-be-flipping-v3: New file.
	* testsuite/libsframe.decode/be-flipping-v3.c: New test.
	* testsuite/libsframe.decode/decode.exp: Run be-flipping-v3.
	* testsuite/libsframe.decode/local.mk: Add be-flipping-v3.
	* testsuite/libsframe.find/find.exp: Run findfre-flex-1.
	* testsuite/libsframe.find/findfre-flex-1.c: New test.
	* testsuite/libsframe.find/local.mk: Add findfre-flex-1.