EGL BlobCache: Update multifile key and value size

Make it clearer what the key and value size limits are.
Base the hot cache on those values, rather than the
other way around.

Test: pubg_mobile_launch ANGLE trace
Test: /data/nativetest64/EGL_test/EGL_test
Test: /data/nativetest64/libEGL_test/libEGL_test
Bug: b/266725576
Change-Id: I337beaf0e01c6497f619c29c01f94242c7b5c959