HPCC-12561 Implement 1st set of xml read improvements

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
>This sharedResult protected by crit seems like a bad idea in general (especially once you have the StringBuffer local fix in place).

I agree, sees bad approach.
I'm not sure if these crit's are also protecting cnv2Latin and routines that it calls (like rtlCodepageConvert) as well though.
I'd guess crits are necessary apart from misguided use to protect sharedResult.