cranelift-filetest: Add support for Wasm-to-CLIF translation filetests (#5412)

This adds support for `.wat` tests in `cranelift-filetest`. The test runner
translates the WAT to Wasm and then uses `cranelift-wasm` to translate the Wasm
to CLIF.

These tests are always precise output tests. The test expectations can be
updated by running tests with the `CRANELIFT_TEST_BLESS=1` environment variable
set, similar to our compile precise output tests. The test's expected output is
contained in the last comment in the test file.

The tests allow for configuring the kinds of heaps used to implement Wasm linear
memory via TOML in a `;;!` comment at the start of the test.

To get ISA and Cranelift flags parsing available in the filetests crate, I had
to move the `parse_sets_and_triple` helper from the `cranelift-tools` binary
crate to the `cranelift-reader` crate, where I think it logically
fits.

Additionally, I had to make some more bits of `cranelift-wasm`'s dummy
environment `pub` so that I could properly wrap and compose it with the
environment used for the `.wat` tests. I don't think this is a big deal, but if
we eventually want to clean this stuff up, we can probably remove the dummy
environments completely, remove `translate_module`, and fold them into these new
test environments and test runner (since Wasmtime isn't using those things
anyways).

cranelift/filetests/filetests/wasm/basic-wat-test.wat

@@ -0,0 +1,42 @@
+;;! target = "x86_64"
+;;!
+;;! [globals.vmctx]
+;;! type = "i64"
+;;! vmctx = true
+;;!
+;;! [globals.heap_base]
+;;! type = "i64"
+;;! load = { base = "vmctx", offset = 0, readonly = true }
+;;!
+;;! [[heaps]]
+;;! base = "heap_base"
+;;! min_size = 0
+;;! offset_guard_size = 0xFFFFFFFF
+;;! index_type = "i32"
+;;! style = { kind = "static", bound = 0x1000 }
+
+(module
+  (memory 0)
+  (func (param i32 i32) (result i32)
+    local.get 0
+    i32.load
+    local.get 1
+    i32.load
+    i32.add))
+
+;; function u0:0(i32, i32, i64 vmctx) -> i32 fast {
+;;     gv0 = vmctx
+;;     gv1 = load.i64 notrap aligned readonly gv0
+;;     heap0 = static gv1, min 0, bound 4096, offset_guard 0xffff_ffff, index_type i32
+;;
+;;                                 block0(v0: i32, v1: i32, v2: i64):
+;; @0021                               v4 = heap_addr.i64 heap0, v0, 0, 4
+;; @0021                               v5 = load.i32 little heap v4
+;; @0026                               v6 = heap_addr.i64 heap0, v1, 0, 4
+;; @0026                               v7 = load.i32 little heap v6
+;; @0029                               v8 = iadd v5, v7
+;; @002a                               jump block1(v8)
+;;
+;;                                 block1(v3: i32):
+;; @002a                               return v3
+;; }