[OpenMP] Add lower and upper bound in num_teams clause

This patch adds lower-bound and upper-bound to num_teams clause
according to OpenMP 5.1 specification. The initial number of teams
created is implementation defined, but it will be greater than or
equal to lower-bound and less than or equal to upper-bound. If
num_teams clause is not specified, the number of teams created is
implementation defined, but it will be greater or equal to 1.

Differential Revision: https://reviews.llvm.org/D95820