Switch from flatKeywordList() to flat arrays

[karlhorky]

Part of preparations for PR #673

Copied from my original comment:

I see there is no distinction in the keyword tokens between all and dataType / datatype / dataTypes:

sql-formatter/src/languages/postgresql/postgresql.keywords.ts

Lines 4 to 8 in 290f3b7

	// https://www.postgresql.org/docs/14/sql-keywords-appendix.html
	all: [
	'ABORT',
	'ABSOLUTE',
	'ACCESS',

sql-formatter/src/languages/transactsql/transactsql.functions.ts

Lines 78 to 83 in 290f3b7

	dataType: [
	'DATALENGTH',
	'IDENT_CURRENT',
	'IDENT_INCR',
	'IDENT_SEED',
	'IDENTITY',

sql-formatter/src/languages/snowflake/snowflake.keywords.ts

Lines 102 to 106 in 290f3b7

	datatypes: [
	'NUMBER',
	'DECIMAL',
	'NUMERIC',
	'INT',

sql-formatter/src/languages/transactsql/transactsql.functions.ts

Lines 303 to 309 in 290f3b7

	// Parameterized types
	// https://docs.microsoft.com/en-us/sql/t-sql/data-types/data-types-transact-sql?view=sql-server-ver15
	dataTypes: [
	'DECIMAL',
	'NUMERIC',
	'FLOAT',
	'REAL',

This is because of the flatKeywordList() function, which effectively discards the key information:

sql-formatter/src/utils.ts

Lines 18 to 20 in 290f3b7

	// Used for flattening keyword lists
	export const flatKeywordList = (obj: Record<string, string[]>): string[] =>
	dedupe(Object.values(obj).flat());

Because of this, I would like to simplify the src/languages/*/*.keywords.ts files to export 1 flat array (with empty lines + comments as separators instead of object keys) and delete the flatKeywordList() function - this will prevent unusual, inconsistent naming conventions and also clarify that the object keys do nothing.

Reviewer notes

1. Best to review this with whitespace changes turned off: https://github.com/sql-formatter-org/sql-formatter/pull/676/files?w=1
2. This PR also enables GitHub Actions workflows CI for pull requests on branches other than master and develop, so that PRs from community members can be tested on GitHub Actions
3. while removing the object keys, I added comments as such:
   a. if there was a commented URL above the key, I removed the key and left the URL as the sole comment (eg. in src/languages/db2i/db2i.functions.ts)
   b. if there was no other comment (or if the commented URL was generic, for multiple sections), I left the key name as the comment (eg. in src/languages/hive/hive.functions.ts)

[nene]

Thanks 👍

[karlhorky]

Glad to help, thanks for the review and merge!