Fix tests broken in commit 77425539.

applet.interface.jtag_probe: fix race condition in scan_xr().

applet.interface.jtag_probe: don't track IR offsets. NFCI. Per-TAP IR offsets are redundant, pointless, and complicate the logic of specifying IR lengths manually.

applet.interface.jtag_probe: improve TAP selection logic. * Require --tap-index option if more than one TAP is found. Before this commit, TAP #0 was implicitly chosen. * Extract redundant error handling code into select_tap(). * Convert logger errors into exceptions where appropriate.

applet.interface.jtag_probe: remove read_dr(idempotent=) argument. Before this commit, this unused option had to be threaded through a lot of unrelated code, which polluted interfaces. Moreover, since commit 42144aa6, it is also worse than useless, because scan_dr() does the exact same thing more safely (it does not rely on provided DR length).

applet.interface.jtag_probe: remove scan_dr(zero_ok=) argument. Before this commit, this option used only in enumerate-ir had to be threaded through a lot of unrelated code, which polluted interfaces and made the logic hard to understand. Also, tighten the post-conditions on scan_xr_length() such that it always requires a valid scan result (finite non-zero length).

applet.interface.jtag_probe: move XR scan limits to JTAGProbeInterface. Before this commit, these rarely useful options had to be threaded through a lot of unrelated code, which polluted interfaces and was done quite inconsistently. Also, do not call add_run_arguments() from add_run_tap_arguments(). This was inconsistent with our conventions and required an `access` argument in add_run_tap_arguments() that was otherwise unnecessary.

applet.interface.jtag_probe: reliably detect overlong XR scans.

applet.interface.jtag_probe: clarify enumerate-ir documentation. Also, lower log level for DR[?] to WARN since it is as noncompliant as DR[0] and neither of these results usually indicates a problem.

cli: make horrifying formatting regexps even more horrifying. Before this commit, lists weren't formatted, which was quite ugly with list items longer than ~70 characters. After this commit, list items are reflowed and their indentation is normalized.