intrinsic-test: sve support

[davidtwco]

This needs rust-lang/rust#157915 to be in nightly for CI to pass - it is already approved and in the bors queue.

This patch contains all the changes necessary for intrinsic-test to generate tests for the SVE intrinsics:

• Some of the commits are just general refactors to the tool, motivated by the commits that follow and that I felt were hard to justify on their own
  • All of the other refactorings have already been landed (intrinsic-test: sve type parsing and constraints #2121, intrinsic-test: run rustfmt on generated sources #2122, intrinsic-test: add lots of documentation #2124, intrinsic-test: refactor populate_random and related code #2126, intrinsic-test: remove arm::argument module #2127)
• Some of the commits are small changes I made along the way (e.g. forwarding args from intrinsic-test.sh to cargo test)
  • I could split these out if we wanted
• Some of the commits modify the definitions of intrinsics so that they pass tests - this only happened for a handful of intrinsics and the changes required to their definitions were very minor
  • I could split these out if we wanted
• Some of the commits update arm_intrinsics.json to add some additional constraints necessary to generate the right tests (we're making sure that these addl. constraints are reflected in the source of truth we use to generate that file internally)
  • I could split these out if we wanted
• Any remaining commits are changes to make the tool generate the correct tests, primarily:
  • Adding the arm_sve.h headers and appropriate target feature flags for C and Rust
  • Using the svld1 intrinsic when loading an argument of scalable vector type
    • There is a special case for svbool_t arguments which do not have an svld1 intrinsic, we load a svint8_t and use svcmpne_n_s8 against zero to produce a svbool_t from it
  • Generating test arrays for intrinsics that take boolean values and svbool_t values (though the earlier commits use the same svptrue_$ty predicate for these arguments initially)
  • Supporting calls to enum-typed const generic arguments (such as svpattern), using simple const functions that map integers from intrinsic-test constraints to the appropriate variant
  • Generating a local containing a predicate that is used by all intrinsics which require a predicate (just svptrue_$ty() to enable every lane)
  • Using svcmpeq_$ty and svptest_any to compare the Rust and C results instead of assert_eq!
    • There is a special-case for tuples of vectors, where multiple svcmpeq_$ty and svptest_any blocks are generated for each vector in the tuple, with svgetN calls to extract the appropriate vector from the result tuples
    • There is also a special-case for intrinsics that return svbool_t, where there is no equivalent svcmpeq_$ty call, so sveor_b_z (exclusive OR) and !svptest_any is used
    • There is yet another special case for scalable vectors of floats, where the pre-existing NanEqF* type cannot be used, so a (rust == c) || (isnan(rust) && isnan(c)) check is performed instead, via a handful of SVE intrinsics
• I haven't been been able to test this on x86 to check that I haven't broken the test generation, but I don't think I've made any changes to the generated output that weren't in the Arm-specific parts