DEV: correct a few Ruby 2.7 deprecations

Note:

```
def foo(bar: 1)
end

foo({bar: 2})
# raises a deprecation, instead use:

foo(**{bar: 2})
```

Additionally when matching regexes always use strings. It does not make
sense to match a non string to a regex.

app/controllers/metadata_controller.rb

@@ -25,7 +25,13 @@ class MetadataController < ApplicationController
   private
 
   def default_manifest
-    display = Regexp.new(SiteSetting.pwa_display_browser_regex).match(request.user_agent) ? 'browser' : 'standalone'
+    display = "standalone"
+    if request.user_agent
+      regex = Regexp.new(SiteSetting.pwa_display_browser_regex)
+      if regex.match(request.user_agent)
+        display = "browser"
+      end
+    end
 
     manifest = {
       name: SiteSetting.title,

app/controllers/reviewables_controller.rb

@@ -33,8 +33,8 @@ class ReviewablesController < ApplicationController
       filters[filter_key] = params[filter_key]
     end
 
-    total_rows = Reviewable.list_for(current_user, filters).count
-    reviewables = Reviewable.list_for(current_user, filters.merge(limit: PER_PAGE, offset: offset)).to_a
+    total_rows = Reviewable.list_for(current_user, **filters).count
+    reviewables = Reviewable.list_for(current_user, **filters.merge(limit: PER_PAGE, offset: offset)).to_a
 
     claimed_topics = ReviewableClaimedTopic.claimed_hash(reviewables.map { |r| r.topic_id }.uniq)
 

app/controllers/topics_controller.rb

@@ -449,7 +449,7 @@ class TopicsController < ApplicationController
     topic_status_update = topic.set_or_create_timer(
       status_type,
       params[:time],
-      options
+      **options
     )
 
     if topic.save

app/models/remote_theme.rb

@@ -146,7 +146,7 @@ class RemoteTheme < ActiveRecord::Base
     importer.all_files.each do |filename|
       next unless opts = ThemeField.opts_from_file_path(filename)
       value = importer[filename]
-      updated_fields << theme.set_field(opts.merge(value: value))
+      updated_fields << theme.set_field(**opts.merge(value: value))
     end
 
     # Destroy fields that no longer exist in the remote theme

lib/user_name_suggester.rb

@@ -11,7 +11,7 @@ module UserNameSuggester
   end
 
   def self.parse_name_from_email(name_or_email)
-    return name_or_email if name_or_email !~ User::EMAIL
+    return name_or_email if name_or_email.to_s !~ User::EMAIL
 
     # When 'walter@white.com' take 'walter'
     name = Regexp.last_match[1]