`memory read` will return an error if you try to read more than 1k bytes
in a single command, instructing you to set
`target.max-memory-read-size` or use `--force` if you intended to read
more than that. This is a safeguard for a command where people are being
explicit about how much memory they would like lldb to read (either to
display, or save to a file) and is an annoyance every time you need to
read more than a small amount. If someone confuses the --count argument
with the start address, lldb may begin dumping gigabytes of data but I'd
rather that behavior than requiring everyone to special-case their way
around a common use case.

I don't want to remove the setting because many people have added (much
larger) default max read sizes to their ~/.lldbinit files after hitting
this behavior. Another option would be to stop reading/using the value
in Target.cpp, but I see no harm in leaving the setting if someone
really does prefer to have a small cap on their memory read size.

TargetProperties.td had a few settings listed as signed integral values,
but the Target.cpp methods reading those values were reading them as
unsigned. e.g. target.max-memory-read-size, some accesses of
target.max-children-count, still today, previously
target.max-string-summary-length.

After Jonas' change to use templates to read these values in
https://reviews.llvm.org/D149774, when the code tried to fetch these
values, we'd eventually end up calling OptionValue::GetAsUInt64 which
checks that the value is actually a UInt64 before returning it; finding
that it was an SInt64, it would drop the user setting and return the
default value. This manifested as a bug that target.max-memory-read-size
is never used for memory read.

target.max-children-count is less straightforward, where one read of
that setting was fetching it as an int64_t, the other as a uint64_t.

I suspect all of these settings were originally marked as SInt64 so a
user could do -1 for "infinite", getting it static_cast to a UINT64_MAX
value along the way. I can't find any documentation for this behavior,
but it seems like something Greg would have done. We've partially lost
that behavior already via
https://github.com/llvm/llvm-project/pull/72233 for
target.max-string-summary-length, and this further removes it.

We're still fetching UInt64's and returning them as uint32_t's but I'm
not overly pressed about someone setting a count/size limit over 4GB.

I added a simple API test for the memory read setting limit.