Classify some project files as XML (#3696)

Also added disambiguation rule for `.proj` and `.user`.

##### CSCFG

https://github.com/search?utf8=%E2%9C%93&q=extension%3Acscfg+NOT+nothack&type=Code
(16.7K hits)

##### CSDEF

https://github.com/search?utf8=%E2%9C%93&q=extension%3Acsdef+NOT+nothack&type=Code
(12.7K hits)

##### CCPROJ

https://github.com/search?utf8=%E2%9C%93&q=extension%3Accproj+NOT+nothack&type=Code
(5K hits)

##### DEPPROJ

https://github.com/search?utf8=%E2%9C%93&q=extension%3Adepproj+NOT+nothack&type=Code
(505 hits)

##### NDPROJ

https://github.com/search?utf8=%E2%9C%93&q=extension%3Andproj+NOT+nothack&type=Code
(194 hits)

##### PROJ

https://github.com/search?utf8=%E2%9C%93&q=extension%3Aproj+%28project+OR+Property+OR+Import+OR+xml+OR+xmlns%29&type=Code
(35K hits)

##### SHPROJ

https://github.com/search?utf8=%E2%9C%93&q=extension%3Ashproj+NOT+nothack&type=Code
(13K hits)

lib/linguist/languages.yml

@@ -4865,12 +4865,16 @@ XML:
   - ".ant"
   - ".axml"
   - ".builds"
+  - ".ccproj"
   - ".ccxml"
   - ".clixml"
   - ".cproject"
+  - ".cscfg"
+  - ".csdef"
   - ".csl"
   - ".csproj"
   - ".ct"
+  - ".depproj"
   - ".dita"
   - ".ditamap"
   - ".ditaval"
@@ -4893,6 +4897,7 @@ XML:
   - ".mm"
   - ".mod"
   - ".mxml"
+  - ".ndproj"
   - ".nproj"
   - ".nuspec"
   - ".odd"
@@ -4900,6 +4905,7 @@ XML:
   - ".pkgproj"
   - ".plist"
   - ".pluginspec"
+  - ".proj"
   - ".props"
   - ".ps1xml"
   - ".psc1"
@@ -4910,6 +4916,7 @@ XML:
   - ".sch"
   - ".scxml"
   - ".sfproj"
+  - ".shproj"
   - ".srdf"
   - ".storyboard"
   - ".stTheme"