meson: Use the standard dependency mechanism to find bzip2

This follows standard conventions in Meson by using the pkg-config file.
This change allows Conan to switch to the Meson build system.

meson.build

@@ -316,8 +316,10 @@ else
 endif
 
 # BZip2 support
-bzip2_dep = cc.find_library('bz2',
-  required: get_option('bzip2'))
+bzip2_dep = dependency('bzip2', required: false)
+if not bzip2_dep.found()
+  bzip2_dep = cc.find_library('bz2', has_headers: ['bzlib.h'], required: get_option('bzip2'))
+endif
 
 if bzip2_dep.found()
   ftoption_command += ['--enable=FT_CONFIG_OPTION_USE_BZIP2']