Message placeholder adjustments

Description

This ticket proposes the addition of structured transform rules targeted at improving message placeholder replacement. It allows for tuning around the boundaries of inserted placeholders, to handle changes like inserting spaces between Chinese and Latin placeholders.

This can also be used in CLDR text with placeholders, such as list formats.

Messages with placeholders often suffer because the replacement of a placeholder also demands certain changes to the text around the placeholder. Example:

Message pattern: "I want a {THING}"
Replacement: "apple"
Desired result: "I want an apple"
Actual result: "I want a apple"

In many cases, the changes are quite extensive, and require a more sophisticated grammatical approach. However, il meglio è l'inimico del bene: for messages without a powerful engine behind them, we can substantially improve the quality. The key is transform data to do small, targeted changes to the text around the placeholder replacement boundaries that result in improvements in the vast majority* of cases.

Vast majority needs some explaining. Suppose in a particular language, an 'h' is silent 95% of the time. In that language, a rule that changes "la |h" to "l’h" (where | represents a replacement boundary) could be better 95% of the time, and worse 5% of the time. The goal is to have cases of better quality swamp the cases of worse quality.

Of course, we would need any such rules to be vetted by native speakers.

Some possible examples:

Language	Format string	Current behavior	Expected behavior	Rule
English	I want a {OBJECT}	I want a book I want a apple	I want a book I want an apple	a->an if followed by a vowel or h+vowel
Russian	О {OBJECT}	О программе О акции	О программе Об акции	о->об if followed by a vowel
Belarusian	{PERSON} удзельнічае	Алег удзельнічае Вольга удзельнічае	Алег удзельнічае Вольга ўдзельнічае	у->ў if preceded by a vowel
Armenian	{OBJECT}n	Katun Girkn	Katun Girke	Definitive article. n->e if preceded by a consonant and forms one word
French	Avez-vous apprécié votre voyage à {PLACE}	Avez-vous apprécié votre voyage à le Japon Avez-vous apprécié votre voyage à les États-Unis	Avez-vous apprécié votre voyage au Japon Avez-vous apprécié votre voyage aux États-Unis	“à le”-> “au” “à les” ->”aux”
German	“In {PLACE}”	In die Stadt In dem Haus	In die Stadt Im Haus	“in dem” -> “im”
Spanish	“A {PLACE}”	A el museo	Al museo	“a el” -> “al”, “de el” -> “del”
Korean	{PERSON}은(는)	철수은(는) 정식은(는)	철수는 정식은	"은(는)" -> "는" or “은" depending on the previous syllable ends with a consonant or not.