liblog: event log tags cache miss call logd for update

Deal with cache miss in the event tag map resources and switch to
"Plan B" to ask long-path to logd for a determination on the tag,
name and format.

logcat-unit-tests liblogcat.descriptive does an under-the-hood call
to logd to add a new logtag but the in-process mapping fails to
pick it up because the /dev/event-tag-map map is SHARED PRIVATE for a
few moments to garner some (linux) efficiency with other copies that
are in the process.  Without the workaround of marking the mapping
dirty to be reread, we are using this change as the proper workaround
that fixes the later parts of this test.

Test: gTest logcat-unit-tests --gtest_filter=liblogcat.descriptive
Bug: 31456426
Bug: 35326290
Change-Id: Ibe54d4df00ed92248e1e644ecebc95f60b222b4d

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