v3.2.7.26_release_20210730

主要修改内容：
（1）pag内部架构调整，为移除skia依赖做准备；
（2）解决由于CheckGLError导致空指针所造成的Crash;
（3）将 Context 上 GPU 资源的清理改成外部 调用 releaseAll() 来触发，避免在析构函数里执行清理导致跟 Resource 的释放发生线程安全问题;
（4） 内存申请由new修改为malloc，避免Android端内存不足时crash
（5）修复模糊度变化也使用缩放导致锯齿的问题
（6）iOS端进后台finish的时候makeCurrent要加锁
（7）context可以被多个PAGSurface持有，grContext被abandon之后，影响其他surface问题修复

Main revisions:
（1） Pag internal architecture adjustment to prepare for removing skia dependency;
（2） Solve the crash caused by null pointer due to CheckGLError;
（3）Change the cleanup of GPU resources on Context triggered by calling releaseAll() externally to avoid cleaning up in the destructor and causing thread safety issues with the release of Resource;
（4） Memory application is changed from new to malloc to avoid crash when the Android side has insufficient memory
（5）Fix the issue of aliasing caused by changes in blur using scaling
（6） makeCurrent needs to be locked when the iOS end enters the background to finish
（7） Because context can be held by multiple PAGSurfaces, fix the problem of grContext affecting other surfaces after being abandoned.