Tests: use JS-compatible module names

When the core tests are converted to JS, module names are used as JS
identifiers, so "-" is not a valid symbol in that context. Use "_"
instead.

Author: thibaudmichaud

test/core/stack-switching/cont.wast

@@ -574,7 +574,7 @@
 
 ;; Nested example: generator in a thread
 
-(module $concurrent-generator
+(module $concurrent_generator
   (func $log (import "spectest" "print_i64") (param i64))
 
   (tag $syield (import "scheduler" "yield"))

test/core/stack-switching/validation_gc.wast

@@ -228,7 +228,7 @@
 ;;;;
 
 
-(module $subtyping-resume0
+(module $subtyping_resume0
 
   (type $ft0 (func))
   (type $ct0 (cont $ft0))
@@ -260,7 +260,7 @@
   )
 )
 
-(module $subtyping-resume1
+(module $subtyping_resume1
 
   (type $ft0 (func))
   (type $ct0 (cont $ft0))