Fix transform controls

[chapulina]

🦟 Bug fix

Summary

Since gazebosim/gz-gui#295, the "click" events are only emitted on release. For press and drag, new events are needed.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[codecov]

Codecov Report

Merging #1081 (042112e) into ign-gazebo6 (9d6157e) will decrease coverage by 0.05%.
The diff coverage is 22.22%.

@@               Coverage Diff               @@
##           ign-gazebo6    #1081      +/-   ##
===============================================
- Coverage        64.12%   64.06%   -0.06%     
===============================================
  Files              255      255              
  Lines            19994    20002       +8     
===============================================
- Hits             12821    12815       -6     
- Misses            7173     7187      +14     

Impacted Files	Coverage Δ
.../gui/plugins/transform_control/TransformControl.cc	7.34% <22.22%> (+0.36%)	⬆️
...int_position_controller/JointPositionController.cc	53.14% <0.00%> (-5.15%)	⬇️
src/EntityComponentManager.cc	85.48% <0.00%> (+0.13%)	⬆️

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[iche033]

fixes the transform issue for me.

I noticed in this branch, there are more camera jumps if I drag the mouse to pan / orbit the camera quickly, especially the very first click and drag after launch. This can be addressed separately.