Add clang-format file

[jimying]

It could help contributors and avoid useless code style reviews.

[jimying]

According to Coding Convention,

It can be expanded on this basis

---
BasedOnStyle: LLVM

IndentWidth: 4
TabWidth:   8   
UseTab: AlignWithSpaces
BreakBeforeBraces: Linux
ColumnLimit: 80
IndentCaseLabels: false

# Disable single line
AllowShortFunctionsOnASingleLine: None
AllowShortIfStatementsOnASingleLine: Never
AllowShortBlocksOnASingleLine : false
AllowShortCaseLabelsOnASingleLine: false
AllowShortLoopsOnASingleLine: false 
AllowShortEnumsOnASingleLine: false

# Function params
AllowAllParametersOfDeclarationOnNextLine: false
BinPackParameters: false

[sauwming]

We use editorconfig in #3210.