#13338 Add support for playback of requested Live TV channel from Frontend Services API

[JRRandall]

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[JRRandall]

Needs to be tested. Simple change to extend the Frontend Services API with a method for requesting Live TV playback tuned to a specific channel ID.

• Makes sure requested ChanID is "valid" i.e. non-negative, non-zero.
• Checks current state of frontend GUI and attempts to change to Live TV.
• If current state is Live TV then requested channel identifier passed to network control for tuning.

[JRRandall]

This is the ticket for this pull request. https://code.mythtv.org/trac/ticket/13338

[bennettpeter]

1). I get compile errors

services/frontend.cpp: In member function ‘virtual bool Frontend::PlayLiveTV(int)’:
services/frontend.cpp:206:37: error: ‘jumpMap’ was not declared in this scope
  206 |         GetMythMainWindow()->JumpTo(jumpMap["Live TV"]);
      |                                     ^~~~~~~
services/frontend.cpp:210:35: error: ‘FE_LONG_TO’ was not declared in this scope
  210 |         while ((timer.elapsed() < FE_LONG_TO) &&
      |                                   ^~~~~~~~~~

2). There is already a frontend service that starts Live TV, but always in the last channel played:
http://rocinante:6547/Frontend/SendAction?Action=Live%20TV
There is an optional Value already in that service, not used for Live TV, that could be used for passing in a channum or chanid. This is another way this functionality may be able to be added.