infra: relocate the tools folder.

Collect only library source code in src

meson.build

@@ -138,6 +138,7 @@ headers = [include_directories('inc'), include_directories('.')]
 
 subdir('inc')
 subdir('src')
+subdir('tools')
 
 if get_option('examples') == true
     subdir('examples')

src/meson.build

@@ -71,6 +71,3 @@ pkg_mod.generate(
     filebase     : 'thorvg',
     description  : 'A Thor library for rendering vector graphics'
 )
-
-subdir('tools')
-