Add assume filename flag to clang-format arguments
Add assume filename flag to clang-format arguments

When using stdin as the input source for clang-format, it takes an
--assume-filename argument to determine which language to choose for
formatting. Without this flag, clang-format may assume that the input
text is cpp code and incorrectly apply formatting rules.

zxh0/vscode-proto3,zxh0/vscode-proto3