Update the syntax of where clauses in the Checked C spec

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#967

---

Update the following in the section on where clause in the Checked C spec:

1. Add the description of the new keyword _And that is used to separate two where clause facts:

where-clause:
  where-clause-fact [_And where-clause-fact]

2. Update the syntax of the where-clause-fact to:

where-clause-fact:
  bounds-expression
  equality-expression equality-op equality-expression

3. Add the syntax of equality-expression from the C11 spec:

equality-expression:
  relational-expression
  equality-expression == equality-expression
  equality-expression != equality-expression