[pgAdmin][RM5133] UI Improvements for White and Dark Theme

Hi Hackers,

Attached is the patch to make improvements in the UI for both default and dark themes. Changes include:

1) All the checkboxes are customized now to use theme colors.

2) Switch boxes will use newly introduced ternary color as the off color instead of primary.

2) "No data" status UI change on dependents, dependency, properties and other places.

3) Event trigger -> Definition input fields UI changes. Document changed.

4) Schema diff cosmetic improvements along with support for dark theme.

5) Improve Style of Dark Mode Code Highlight After Query Execution. Fixes #4996.

6) Background for geometry viewer changed to use #fff for all themes. This will allow it to look cleaner. Fixes #5077.

7) Select2 dropdown selected and hovered item should will have different colors. Also tweaked the tags appearance in multi select boxes. Fixes #4955.

8) Source code pro font updated to latest version to fix firefox monospace issue. Fixes #5184.

9) Other accessibility and cosmetic changes wherever needed.

Thanks @Chethana Kumar for your suggestions and inputs. :)

Kindly review.