Add tm-http-request message for making HTTP requests (#7422)

* Initial Commit

* HttpClient object shouldn't need to know about events

* Add support for cancelling HTTP requests

* Make the number of outstanding HTTP requests available in a state tiddler

* Add a network activity button

Click it to cancel outstanding requests

* Fix typo

Thanks @btheado

Co-authored-by: btheado <brian.theado@gmail.com>

* Fix crash when cancelling more than one HTTP request

Thanks @saqimtiaz

* Further fixes to cancelling outstanding HTTP requests

* Fix missing body

---------

Co-authored-by: btheado <brian.theado@gmail.com>

core/ui/PageControls/network-activity.tid

@@ -0,0 +1,16 @@
+title: $:/core/ui/Buttons/network-activity
+tags: $:/tags/PageControls
+caption: {{$:/core/images/network-activity}} {{$:/language/Buttons/NetworkActivity/Caption}}
+description: {{$:/language/Buttons/NetworkActivity/Hint}}
+
+\whitespace trim
+<$button message="tm-http-cancel-all-requests" tooltip={{$:/language/Buttons/NetworkActivity/Hint}} aria-label={{$:/language/Buttons/NetworkActivity/Caption}} class=<<tv-config-toolbar-class>>>
+<$list filter="[<tv-config-toolbar-icons>match[yes]]">
+{{$:/core/images/network-activity}}
+</$list>
+<$list filter="[<tv-config-toolbar-text>match[yes]]">
+<span class="tc-btn-text">
+<$text text={{$:/language/Buttons/NetworkActivity/Caption}}/>
+</span>
+</$list>
+</$button>