Light/Dark Visual Studio theme needs improvements to handle expressions in template string. Fixes #13166

fixes #14987

fixes #14949

* Make markdown image dimensions configurable using a custom image renderer

In the newly introduced syntax extension the width and height of an image
can be given in the image title using following format:
![image](someimageurl 'caption|height=200, width=100').
Both width and height parameters are optional, if they are not given the
width and height attributes remains unset on the image element

This resolves #14803

* Change size parameter location to href part

- Disable replace action
- Do not remove the match to replace. Model update does it anyways
- Update the matches for the line after replace