LibGUI/FileIconProvider: Add config file and use patterns

This moves file extension to icon mappings from compile time macros to an
INI config file (/etc/FileIconProvider.ini), so file icons can easily be
customized and extended :^)

I also switched the format from a static file extension (".foo") to
glob-like patterns ("*.foo", using StringUtils::matches()), which allows
us to assign icons to specific exactly matching file names, like many
IDEs do - e.g. "CMakeLists.txt" or ".prettierrc".

Base/etc/FileIconProvider.ini

@@ -0,0 +1,18 @@
+[Icons]
+cplusplus=*.cpp,*.cxx,*.cc,*.c++
+form=*.frm
+hackstudio=*.hsp
+header=*.h,*.hpp,*.hxx,*.hh,*.h++
+html=*.html,*.htm
+ini=*.ini
+java=*.java
+javascript=*.js,*.mjs
+library=*.so,*.a
+markdown=*.md
+music=*.midi
+object=*.o,*.obj
+pdf=*.pdf
+python=*.py
+sound=*.wav
+spreadsheet=*.sheets
+text=*.txt