Fix Dart API generation bugs; Add ability to generate API for path parameters (#2887)

* Fix bug in dartgen: Import path should match the generated api filename

* Use Route.HandlerName as generated dart API function name

Reasons:
- There is bug when using url path name as function name, because it may have invalid characters such as ":"
- Switching to HandlerName aligns with other languages such as typescript generation

* [DartGen] Add ability to generate api for url path parameters such as /path/:param

tools/goctl/api/dartgen/vars.go

@@ -3,13 +3,16 @@ package dartgen
 import "text/template"
 
 var funcMap = template.FuncMap{
-	"getBaseName":           getBaseName,
-	"getPropertyFromMember": getPropertyFromMember,
-	"isDirectType":          isDirectType,
-	"isClassListType":       isClassListType,
-	"getCoreType":           getCoreType,
-	"pathToFuncName":        pathToFuncName,
-	"lowCamelCase":          lowCamelCase,
+	"getBaseName":                     getBaseName,
+	"getPropertyFromMember":           getPropertyFromMember,
+	"isDirectType":                    isDirectType,
+	"isClassListType":                 isClassListType,
+	"getCoreType":                     getCoreType,
+	"lowCamelCase":                    lowCamelCase,
+	"normalizeHandlerName":            normalizeHandlerName,
+	"hasUrlPathParams":                hasUrlPathParams,
+	"extractPositionalParamsFromPath": extractPositionalParamsFromPath,
+	"makeDartRequestUrlPath":          makeDartRequestUrlPath,
 }
 
 const (