Rename buildSnapshot to buildScriptSnapshot (#16905)
Rename buildSnapshot to buildScriptSnapshot (#16905)

Renames buildSnapshot to build buildScriptSnapshot in preparation for
AOT snapshot tests.
cbracken/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter