Allow non-integer RANGE in OVER

Allow non-integer RANGE in OVER

Updated the :func:`_sql.over` clause to allow non-integer values in
:paramref:`_sql.over.range_` clause. Previously, only integer values
were allowed and any other values would lead to a failure.
To specify a non-integer value, use the new :class:`_sql.FrameClause`
construct along with the new :class:`_sql.FrameClauseType` enum to specify
the frame boundaries.

Fixes #12596.
Closes: #12695
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12695
Pull-request-sha: 8063cec65d1e7ad5d640bf689c01079e2d8c89ae

Change-Id: I248a938f6502d72555c005d86791c992822117d4