Set editor font in a such a way that it doesn't need to be reset by widgets (e.g. find widget)

[alexdima]

e.g. #5154 (comment)

[bpasero]

@alexandrudima thanks for picking this up, I still see some places where we have to copy the font-family into the CSS:

• https://github.com/Microsoft/vscode/blob/master/src/vs/base/browser/ui/inputbox/inputBox.css#L21
• https://github.com/Microsoft/vscode/blob/master/src/vs/editor/contrib/parameterHints/browser/parameterHints.css#L111
• https://github.com/Microsoft/vscode/blob/master/src/vs/editor/contrib/quickFix/browser/quickFix.css#L95
• https://github.com/Microsoft/vscode/blob/master/src/vs/editor/contrib/suggest/browser/suggest.css#L93

[alexdima]

@bpasero Since I don't force it on widgets anymore, I removed the font declarations from the obvious places. We should track these places in separate debt issues going to the owners of those widgets.

[bpasero]

Filed: #6171, #6170 and #6169