Ensure odbc locates SQL Server drivers on macOS running on Apple Silicon. Addresses #892

[stevecondylios]

This updates common_dirs in locate_install_unixodbc() to ensure odbc is able to find database drivers and set the ODBCSYSINI environment variable correctly. It is based on the path to which homebrew installs SQL Server drivers on macOS running on Apple Silicon.

Homebrew is the installation method recommended by Microsoft.

Before change:

odbc::odbcListDrivers()
# [1] name      attribute value    
# <0 rows> (or 0-length row.names)

After change (drivers automatically located by odbc):

odbc::odbcListDrivers()
#                            name   attribute                                   value
# 1 ODBC Driver 18 for SQL Server Description Microsoft ODBC Driver 18 for SQL Server
# 2 ODBC Driver 18 for SQL Server      Driver /opt/homebrew/lib/libmsodbcsql.18.dylib
# 3 ODBC Driver 18 for SQL Server  UsageCount                                       1

[simonpcouch]

Great work, @stevecondylios. Thank you!