[Ide] Fix bug 21254 - Get the encoding from the document content instead of returning Encoding.Default.
[Debugger] Wrap the "Debugger is Busy" dialog

Fixes bug #22730
[Ide] Correct typo in ImageLoader. Fix gravatar images not showing on retina screens.
[Ide] Add new variable to be used in custom tools

Added FileNamePrefix variable which is replaced by the file name without
the extension.

Fixes bug #21342 - In External Tool, make ${FileName} resolve to the file
name without extension, as in VS
Bug 23515 - SVN commit fails every time
[Ide] Fix formatting document removing all XML text.

Fixed bug 20467 - Format document on duplicated attributes removes all text
https://bugzilla.xamarin.com/show_bug.cgi?id=20467

If the XML in the text editor was invalid when the Edit - Format -
Format Document menu was selected the text would be removed from the
text editor.

Now if the XML is invalid the text is not removed. An error is logged
but nothing else happens.

Whilst this could have been fixed in the XmlFormatter with it
returning the original XML unmodified doing so would have meant
that the undo history would change even though the file had not
been modified. The file would also have been shown as edited.
[Refactoring] Fixed slow context menu update.

That's some legacy code - the background parser always validates the
actions for the current position. When doing it manually there it can
interfere with the background task and cause dead locks. (which are
resolved by long timeouts)
Fixed 'Bug 22752 - Assembly Browser Crashes'
[Subversion] Fix Win32 concurrency.

Missed this one, aaaaaaaaaaaaaaaaaaaaaargh.
[Subversion] Fix spam of TooOld/Upgrading dialogs.

Due to SvnClient initializing a new Backend on every check, the value wasn't retained between Status queries.
This is only a temporary fix, the actual fix for this would be abstracting the backend into actual backend code and interop wrappers to simulate SvnSharp.
[Core] Fix project building issue

The project builder is not more aggressive when a project needs to be
unloaded. Instead of just unloading the project element, it now
unloads all projects. This is necessary because the project may reference
other target files that may have been changed, and which can't be
individually unloaded.

Fixes bug #23435 - XS Shared Projects do not work unless you readd reference
Merge pull request #663 from mono/5.5.4-fixes

5.5.4 fixes