The Pine Script online editor supports this keyboard+mouse shortcut and it is a very convenient feature.
For eg. if I have:

COLOR_PROFIT=#00FF00

And many pages below I have:

plot(y, "some title", COLOR_PROFIT)

And I wish to know what COLOR_PROFIT is, or if I want to change it, instead of having to search for it, I can simply Cmd+click on it (on a Mac, probably Ctrl+click on Windows) and the cursor moves to the symbol declaration (it could be a variable, a function, a function parameter or a UDT).

Main Menu -> Go -> Go to Definition and Main Menu -> Go -> Go to Declaration also do not work (they do nothing).

Main Menu -> Go -> Go to Symbol in Editor... that allows searching for a specific symbol declaration would also be useful. This is also supported In Pine Script online editor, by pressing F1 and selecting the Go to Symbol in Editor... menu item.