small fixes and changes in the mouse event handler

[diegostafa]

fixes:

• avoid yanking when holding a selection and clicking on the gutter
• avoid adding breakpoints when clicking on the status bar

changes:

• drag selections/scrolling actions are not blocked by the gutter
• mouse-click to add breakpoints now require the CTRL modifier
• right mouse click will run the command select_references_to_symbol_under_cursor instead of selecting a single character (just because selecting a character with both left and right click felt redundant) change mouse right click action #10699

[the-mikedavis]

Could you move the change to use select_references_to_symbol_under_cursor to a separate PR? The fixes are easy to merge once we take a look but what command we should use for a right click could use some discussion. An LSP-driven feature might not make the most sense since it won't do anything or will print to the statusline when you don't have a language server running