Inline jump tables in parsed br_table instructions (#5755)

As jump tables are used by at most one br_table instruction, inline their definition in those instructions instead of requiring them to be declared as function-level metadata.

cranelift/frontend/src/ssa.rs

@@ -985,10 +985,9 @@ mod tests {
         // Here is the pseudo-program we want to translate:
         //
         // function %f {
-        // jt = jump_table [block2, block1]
         // block0:
         //    x = 1;
-        //    br_table x, block2, jt
+        //    br_table x, block2, [block2, block1]
         // block1:
         //    x = 2
         //    jump block2