graphics/libbpg: 0.9.5 -> 0.9.7

• Re-enabling the default options based on the new defaults in Makefile
• Linking against port installed libx265 (not internal copy)
• Increased the memory size of the JS decoder to 32 MiB and avoid polluting the global namespace.
• Published the Emscripten patches which reduce the size of the generated JS code.
• Faster encoding (x265 is the default encoder and is built in bpgenc).
• Added monochrome support to x265.
• Fixed metadata handling.

PR: 209554
Submitted by: Matthieu Volat <mazhe@alkumuna.eu>