Refactor route functions in BaseService (#2860)

The route helper functions are fairly well isolated from the rest of BaseService, with a few convenient entry points. They are easier to test in isolation.

The way the code was written before, `pathToRegexp` was invoked once for every request, which seems inefficient.

`route` was validated when it was used, though it seems more helpful to validate it up front.

This breaks out `_makeFullUrl`, `_regex`, `_regexFromPath` into new helper functions `makeFullUrl`, `assertValidRoute`, `prepareRoute`, and `namedParamsForMatch`.

It adds validation to route, and updates the services without patterns to include one, in order to pass the new validation rules.

services/github/github-commit-activity.service.js

@@ -23,6 +23,7 @@ module.exports = class GithubCommitActivity extends LegacyService {
   static get route() {
     return {
       base: 'github/commit-activity',
+      pattern: ':interval(y|4w|w)/:user/:repo',
     }
   }
 

services/github/github-commit-status.service.js

@@ -21,6 +21,7 @@ module.exports = class GithubCommitStatus extends LegacyService {
   static get route() {
     return {
       base: 'github/commit-status',
+      pattern: ':user/:repo/:branch/:commit',
     }
   }
 
@@ -28,7 +29,6 @@ module.exports = class GithubCommitStatus extends LegacyService {
     return [
       {
         title: 'GitHub commit merge status',
-        pattern: ':user/:repo/:branch/:commit',
         namedParams: {
           user: 'badges',
           repo: 'shields',

services/github/github-downloads.service.js

@@ -23,6 +23,7 @@ module.exports = class GithubDownloads extends LegacyService {
   static get route() {
     return {
       base: 'github',
+      pattern: '',
     }
   }
 

services/github/github-followers.service.js

@@ -22,6 +22,7 @@ module.exports = class GithubFollowers extends LegacyService {
   static get route() {
     return {
       base: 'github/followers',
+      pattern: ':user',
     }
   }
 
@@ -29,7 +30,6 @@ module.exports = class GithubFollowers extends LegacyService {
     return [
       {
         title: 'GitHub followers',
-        pattern: ':user',
         previewUrl: 'espadrine',
         // https://github.com/badges/shields/issues/2479
         // namedParams: {

services/github/github-forks.service.js

@@ -22,6 +22,7 @@ module.exports = class GithubForks extends LegacyService {
   static get route() {
     return {
       base: 'github/forks',
+      pattern: ':user/:repo',
     }
   }
 

services/github/github-stars.service.js

@@ -23,6 +23,7 @@ module.exports = class GithubStars extends LegacyService {
   static get route() {
     return {
       base: 'github/stars',
+      pattern: ':user/:repo',
     }
   }
 

services/github/github-watchers.service.js

@@ -22,6 +22,7 @@ module.exports = class GithubWatchers extends LegacyService {
   static get route() {
     return {
       base: 'github/watchers',
+      pattern: ':user/:repo',
     }
   }