Store the modifier in the original mouse event to choose between
move and copy drags.

Issue #2556

So that they don't interfere with clicking and dragging

Issue #2556

Issue #4057

Closes #4057

Use findMarks instead of findMarksAt in foldGutter.js to correctly
find marks when a single line is collapsed so that the arrow displays
correctly as collapsed.

Add option 'clearOnEnter' to foldcode.js and default it to true.
This option determines whether the marker added when folding a
line clears when the cursor enters it.

Closes #4042

See https://discuss.codemirror.net/t/width-of-sql-hint-dropdown-in-firefox-is-not-always-correct/757

It breaks document tree rebalancing.

Closes #4032

See https://discuss.codemirror.net/t/dynamically-switch-mode-with-sql-hint-addon-bugs/751

Closes #3796

Closes #3896

Closes #3900

Issue #3983

Closes #4030
Closes #4031

Closes #3926
Closes #4026

To make it clearer that they are updated together

Issue #4028

Closes #3983

Closes #745

This reverts commit 8dbb84f4.

Issue #3127

Add gutters properties (grid-gap, grid-column-gap and grid-row-gap):
https://www.w3.org/TR/css-grid-1/#gutters

Take advantage to add some missing keywors:
* grid and inline-grid: https://www.w3.org/TR/css-grid-1/#grid-containers
* dense: https://www.w3.org/TR/css-grid-1/#grid-auto-flow-property

It's been a while since the list of properties has been updated:
https://drafts.csswg.org/css-grid/#property-index

1. Mention multiplex as a dependency
2. Add ERB as a MIME-type

Closes #4025

Issue #2901

Issue #4022

Closes #4020