Refactor: libcrmcommon: New pcmk__parse_ms()

To replace crm_get_msec().

There are a lot of parsing improvements that would be welcome (see
T841), but we'll have to be careful about making them. We're parsing
user inputs with this function. So changing how we respond to invalid
values, values that contain some garbage at the end, etc., affects user-
facing behavior, even though the function is internal.

This function basically preserves existing behavior for now, including
that it doesn't yet allow negative values. One key difference is that we
no longer use PCMK__PARSE_INT_DEFAULT inside it in any way. The output
argument (dest) remains unchanged if there is any error besides ERANGE.

Ref T841

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>