[C++] Improve SharedExclusiveChecker error messages

[HyukjinKwon]

Describe the enhancement requested

arrow/cpp/src/arrow/io/interfaces.cc

Lines 341 to 342 in b126c6e

	// XXX The error message doesn't really describe the actual situation
	// (e.g. ReadAt() called while Read() call in progress)

Component(s)

C++

[pitrou]

Issue resolved by pull request 48800
#48800