Ensuring consistency in support for the Timestamp data type format in different statements.

[gaoboal]

Describe the feature you'd like

Currently, there is inconsistency in the support for the Timestamp data type format across statements such as insert, select, and load data infile. Furthermore, the documentation lacks comprehensive descriptions in this regard.
Some test cases and examples: https://qiok3h8ob4.feishu.cn/docx/P1LBdzVIeoPSuHxUUBBcgGq9n7c?from=from_copylink

Desired Improvements

1. Support for String Format Timestamps
   Implement support for Timestamps in string format, including parsing, validation, and support for millisecond-level precision. The expected format is: yyyy-MM-dd HH:mm:ss.SS.

2. Support for int64 Format Timestamps
   Extend support to include Timestamps in int64 format.

3. Conversion Support with timestamp Function
   Allow conversion between string/int64 format Timestamps using the timestamp function.

4. Consistent Behavior for Timestamp Columns with Indexes
   Ensure uniform behavior when dealing with Timestamp columns that have indexes.

By implementing these improvements, we aim to enhance consistency and usability across various statements and operations involving Timestamp data types.

[aceforeverd]

#3731: unify row encode impl with codegen row builder, gives consistent and most widely supported format