clang-format: [JS/TS] Properly understand cast expressions.

Many things were wrong:
- We didn't always allow wrapping after "as", which can be necessary.
- We used to Undestand the identifier after "as" as a start of a name.
- We didn't properly parse the structure of the expression with "as"
  having the precedence of relational operators

llvm-svn: 296659