fix(OAS3): relative urls (#5341)

* Added tooling for appending OAS3 relative URLs to selected Server

Info
* Terms of service URL
* Contact URL
* License URL
* External Docs URL

Tag
* Tag External Docs URL

Operation
* Operation External Docs
** Operation Tag


Co-authored-by: Tim Lai <timothy.lai@gmail.com>

src/core/utils/url.js

@@ -0,0 +1,23 @@
+export function isAbsoluteUrl(url) {
+  return url.match(/^(?:[a-z]+:)?\/\//i) // Matches http://, HTTP://, https://, ftp://, //example.com,
+}
+
+export function addProtocol(url) {
+  if(!url.match(/^\/\//i)) return url // Checks if protocol is missing e.g. //example.com
+  return `${window.location.protocol}${url}`
+}
+
+export function buildBaseUrl(selectedServer, specUrl) {
+  if(!selectedServer) return specUrl
+  if(isAbsoluteUrl(selectedServer)) return addProtocol(selectedServer)
+  
+  return new URL(selectedServer, specUrl).href    
+}
+
+export function buildUrl(url, specUrl, { selectedServer="" } = {}) {  
+  if(!url) return
+  if(isAbsoluteUrl(url)) return url
+
+  const baseUrl = buildBaseUrl(selectedServer, specUrl)
+  return new URL(url, baseUrl).href
+}