[PATCH] Fix ICU strength not being honored in collation rules

Hello,

I have run into an issue where specifying the rules argument for "CREATE COLLATION" changes the collation strength to tertiary, even if it is explicitly set in the rules string. I discovered that this is because ucol_openRules is called passing strength UCOL_DEFAULT_STRENGTH, which overwrites whatever is in the rules string with UCOL_TERTIARY.

This fix changes this call to pass UCOL_DEFAULT instead. This way, UCOL_TERTIARY is still specified by default, but the strength explicitly set on the rules string is not overwritten. This is important because there is currently no way to create a collation with custom tailoring rules with strengh other than tertiary.

What happens currently:

CREATE COLLATION my_col (provider = icu, locale = 'und', rules = '', deterministic = false); -- strengh: tertiary
CREATE COLLATION my_col (provider = icu, locale = 'und', rules = '[strength 2]', deterministic = false); -- strength: tertiary
CREATE COLLATION my_col (provider = icu, locale = 'und', rules = '[strength 1]', deterministic = false); -- strength: tertiary

What happens after the patch:

CREATE COLLATION my_col (provider = icu, locale = 'und', rules = '', deterministic = false); -- strengh: tertiary
CREATE COLLATION my_col (provider = icu, locale = 'und', rules = '[strength 2]', deterministic = false); -- strength: secondary
CREATE COLLATION my_col (provider = icu, locale = 'und', rules = '[strength 1]', deterministic = false); -- strength: primary

As this only affects cases where the strength is explicitly set but was previously ignores, I do not think it is a breaking change.

I have successfully compiled and tested PostgreSQL after this change, and it behaves as documented above.

Thank you in advance,

Luis