LayerTraceGenerator: Provide a large enough buffer to generate layer trace

When generating the layer trace, provide
a large enough buffer to store the traces.

Test: generate layer trace from transaction traces
Test: generate layer trace via winscope
Test: atest libsurfaceflinger_tests
Fixes: 234489414

Change-Id: I72ecae0c40c1706a6def033205947d0e7ab01236