Fix issue 5528 (#5605)

* fix parameter error.

* fix float convert to i8 and i16   should extract sign bit.

* add missing regression test file.

* using tmp register.

* float convert i8 will consume more instructions.

* fix worse inst emit size.

* fix worst_case_size.

cranelift/filetests/filetests/runtests/issue5528.clif

@@ -0,0 +1,20 @@
+test interpret
+test run
+target riscv64
+
+function %a(f32) -> i8 system_v {
+block0(v0: f32):
+    v1 = fcvt_to_sint_sat.i8 v0
+    return  v1
+}
+
+; run: %a(-0x1.000006p125) == -128
+
+
+function %b(f32) -> i16 system_v {
+block0(v0: f32):
+    v1 = fcvt_to_sint_sat.i16 v0
+    return  v1
+}
+
+; run: %b(-0x1.000006p125) == -32768