Env Viz: Automatically clear removed lines' breakpoints [Enhancement]

[Cloud7050]

Currently, if a line stops existing due to being removed (eg from deleting ending lines of a program or pasting in a shorter program), but had a breakpoint, the breakpoint no longer shows up but is still remembered. Trying to run the program with such lingering breakpoints causes the following hint and error:

Hint: Misplaced breakpoint at line x. Line x: Missing semicolon at the end of statement

The error may be from trying to evaluate a blank line.

Ways to get the program to run include adding more (blank) lines to the program to reach that breakpoint's line, such that its line now exists again and the breakpoint shows, to click it away, then deleting those added lines. Or, saving then refreshing the page. Therefore, it may be nice/less annoying to have removed lines' breakpoints get automatically cleared.