Log Message:
vala: updated to 0.54.5

Vala 0.54.5
===========
 * Various improvements and bug fixes:
  - codegen:
    + Correctly handle chain up of struct creation methods
    + Use a dedicated EmitContext for _variant_get*() functions
    + gtkmodule: Handle nested closure elements and bind them accordingly
  - vala:
    + NullLiteral is not a valid argument for string concatenation
    + Set is_yield_expression in async context when chaining up to async base ctor
    + Report statement parsing error if it is not meant to be an expression
    + girparser: Avoid possibily creating duplicated attributes
  - vapigen.m4: use $PKG_CONFIG_SYSROOT_DIR

 * Bindings:
  - glib-2.0: Always use the actual C type for CCode.array_length_type
  - gstreamer: Cherry-pick bindings fixes from 0.56
  - gstreamer-1.0: Unskip the ElementFactory.make/create_full() symbols