windows: expand environment vars in find_exe
This allows us to use ${ProgramFiles} in our [merge-tools] sections so
we can provide locale safe program paths.
[('string', 'string value'), ('bool1', 'true'), ('bool2', 'false')]
[('list1', 'foo'), ('list2', 'foo bar baz'), ('list3', 'alice, bob'), ('list4', 'foo bar baz alice, bob')]
---
'string value'
'true'
'false'
None
---
values.string not a boolean ('string value')
True
False
False
False
True
---
['foo']
['foo', 'bar', 'baz']
['alice', 'bob']
['foo', 'bar', 'baz', 'alice', 'bob']
['foo', 'bar', 'baz', 'alice', 'bob']
[]
[]
['foo']
['foo']
['foo', 'bar']
['foo', 'bar']
['foo bar']
['foo', 'bar']
None
True