option to report dynamic() cast (from overloaded specs)

Summary:
We already had the pieces (and it's reported as an error in strict mode), exposing an env option.

```
EQWALIZER_OVERLOADED_SPEC_DYNAMIC_RESULT=true elp eqwalize-all
```

Result:
P1476661324 (1313 errors)

Reviewed By: VLanvin

Differential Revision: D59646202

fbshipit-source-id: 3888ed8c860d626afc995e204ee1285fd08fae71

Author: ilya-klyuchnikov

eqwalizer/src/main/resources/application.conf

@@ -19,4 +19,6 @@ eqwalizer {
     error_depth = ${?EQWALIZER_ERROR_DEPTH}
     clause_coverage = true
     clause_coverage = ${?EQWALIZER_CLAUSE_COVERAGE}
+    overloaded_spec_dynamic_result = false
+    overloaded_spec_dynamic_result = ${?EQWALIZER_OVERLOADED_SPEC_DYNAMIC_RESULT}
 }

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/package.scala

@@ -47,6 +47,7 @@ package object eqwalizer {
       tolerateErrors: Boolean,
       checkRedundantGuards: Boolean,
       clauseCoverage: Boolean,
+      overloadedSpecDynamicResult: Boolean,
       mode: Mode.Mode,
       errorDepth: Int,
   ) {
@@ -78,6 +79,7 @@ package object eqwalizer {
       tolerateErrors = config.getBoolean("tolerate_errors"),
       checkRedundantGuards = config.getBoolean("check_redundant_guards"),
       clauseCoverage = config.getBoolean("clause_coverage"),
+      overloadedSpecDynamicResult = config.getBoolean("overloaded_spec_dynamic_result"),
       mode,
       errorDepth = config.getInt("error_depth"),
     )

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/tc/ElabApplyOverloaded.scala

@@ -33,7 +33,7 @@ class ElabApplyOverloaded(pipelineContext: PipelineContext) {
         val resTy = elabApply.elabApply(check.freshen(ft), args, argTys, env1)
         (resTy, env1)
       case _ =>
-        if (!pipelineCtx.gradualTyping)
+        if (!pipelineCtx.gradualTyping || pipelineCtx.overloadedSpecDynamicResult)
           diagnosticsInfo.add(NoSpecialType(expr.pos, expr, argTys))
         (DynamicType, env1)
     }

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/tc/package.scala

@@ -73,5 +73,6 @@ package object tc {
     val errorDepth: Int =
       options.errorDepth.getOrElse(config.errorDepth)
     val clauseCoverage: Boolean = config.clauseCoverage
+    val overloadedSpecDynamicResult: Boolean = config.overloadedSpecDynamicResult
   }
 }

eqwalizer/src/test/resources/application.conf

@@ -15,4 +15,6 @@ eqwalizer {
     mode = ${?EQWALIZER_MODE}
     clause_coverage = false
     clause_coverage = ${?EQWALIZER_CLAUSE_COVERAGE}
+    overloaded_spec_dynamic_result = false
+    overloaded_spec_dynamic_result = ${?EQWALIZER_OVERLOADED_SPEC_DYNAMIC_RESULT}
 }