Defer Meshed creation

Refactored Mesh API to defer creation of
SkMesh instances until a GrDirectContext
can be obtained on the RenderThread.
This creates an SkMesh during the prepare
tree step when the UI thread is blocked
to ensure no concurrency issues.

Bug: b/265044322
Test: atest CtsUiRenderingTestCases:MeshTest
Change-Id: Ica8c364b99952e0ee71f7b95b312cf29c51ebc2a