args: use non-capturing groups when joining multiple patterns

[gofri]

Fixes #2480

Fix the joined pattern so that multiple VALID patterns cannot affect each other.
e.g. worked before but fixed now:
echo FooBar | rg -e '(?i)notfoo' -e bar # no result

Wontfix the joined pattern to handle some cases of multiple INVALID patterns that are "coordinated" to fix each other.
e.g. still works but is unexpected:
echo 'FooBar' | rg -e '(' -e ')' # matches with an empty string

also, introduces a new class of invalid patterns that work now but wouldn't work before:
e.g. got parse error before but not now:
echo 'FooBar' | rg ')(' # matches with an empty string

edit: pushed another commit to avoid the regerssion for a single pattern.
the new class still applies for multiple patterns:
e.g. got parse error before but not now:
echo 'FooBar' | rg -e ')(' -e 'x' # matches with an empty string

[gofri]

@BurntSushi I figured the new case just after creating the PR:

also, introduces a new class of invalid patterns that work now but wouldn't work before:
e.g. got parse error before but not now:
echo 'FooBar' | rg ')(' # matches with an empty string

IMHO:
It's not too bad to have this new class for multiple patterns, but I really don't like the fact that it also affects the detection for a single pattern (namely, )().
let me know if you think I should handle len(patterns) == 1 differently

edit: I pushed the commit to fix it, so let me know if you prefer that I revert it.