Option to normalize casing of identifiers in the ScriptGenerator

首先定位 ScriptGenerator 及其当前设置，然后跟踪标识符在生成的 SQL 中是如何输出的。确认大小写是否统一应用，还是需要分别设置实例级和数据库级配置；完成标准是 PreserveOriginal 仍为默认值，并且 LowerCase 和 UpperCase 按照指定使用不变大小写。

SQL Server compares identifiers with respect to the CI/CS, AI/AS setting of the respective database's collation. While accent sensitivity has no effect on the SQL source code, case-sensitivity may have such an effect when the goal is to produce a 'canonical' form of the source code. The locale part of the collation plays no part in this.

Hence, the settings of the ScriptGenerator should be extended with an option to normalize casing of identifiers as follows:

• PreserveOriginal — outputs identifiers as-is; this shall be the default behavior corresponding to the current state (no breaking change)
• LowerCase — lower-case all identifiers when producing the output
• UpperCase — upper-case all identifiers when producing the output

A simple ToLowerInvariant() / ToUpperInvariant() should be used.

Question is, whether the ScriptGenerator should support separate settings for instance-level (global) objects versus objects in a database. This would significantly increase the complexity. See also Database identifiers:

The collation of an identifier depends on the level at which it's defined. Identifiers of instance-level objects, such as logins and database names, are assigned the default collation of the instance. Identifiers of objects in a database, such as tables, views, and column names, are assigned the default collation of the database.