TextUtils.formatDate: take DateFormat not DisplayOptions

[s-leroux]

TextUtils.formatDate takes DisplayOptions but is a low-level helper; pulling date.format from broad options couples date rendering to global display config.

Location: src/displayable.mts:350

Code:

// XXX formatDate is a low-level function that should take DateFormat as argument, not DisplayOptions

Possible approach: Split API: formatDate(date: Date | number, format: DateFormat) and keep a thin wrapper for DisplayOptions at call sites that need it.

[s-leroux]

We need to clarify the status and relationships of the various date-to-string utilities.

Possibly:

• purely utilitarian conversion belongs to Date or TextUtils.
• toDisplayString should support date format as an option.
  Related to displayable.toDisplayString: number formatting for primitives #225.

Out of scope for this issue is the unification of data formats (which are example-based YYYY-MM-DD) and numeric formats (that use specifiers like {+06.2}).