Syntax-coloring is not applied or removed when changing Build Action from None to Compile and vv

Since out-of-project files are no longer colored (inverse to this issue #1977 may have you believe), there now appears to be a small issue with that: it doesn't work when the project has dirty state, it only works if you compile.


## Repro steps

Basically:

1. Open any project *.fs file
2. Change the _Build Action_ to `None`
3. Result: no effect

You can try to close/reopen the file, but still no effect.

The inverse is also true: change from None to Compile will not color the file.

## Expected behavior

Since this change was applied (#1977, possibly it's VS2017, not just Visual F#), this expected behavior is different now: it should remove the coloring, or inverse, it should add the coloring back.

## Actual behavior

Syntax coloring, or removing of coloring is not applied.

## Known workarounds

Recompile the project.

## Related information

F# 4.0 and F# 4.1 with VS2017 15.3.1.0. Also observed in recent nightlies.

A small issue, I know, but I thought to better have it reported in case somebody is working on something in this area.