Add support for readonly & T

[MaryamZi]

Description:
$title.

See ballerina-platform/ballerina-spec#476.

[MaryamZi]

#22965 introduced support for T & readonly.

Closing this issue since the remaining sub-tasks are being tracked with other issues.

• Support T & readonly for table types Support T & readonly for table types #23032
• Disallow langlib methods that modify the value on immutable values Disallow langlib methods that modify the value on immutable values  #22964
• Allow constructing values with their read-only bit on with a type-cast-expr <readonly> Allow constructing values with their read-only bit on with a type-cast-expr <readonly> #22954
• Allow using the type-test for readonly with selectively immutable basic types Allow using the type-test for readonly with selectively immutable basic types #22785
• Support readonly record fields Support readonly record fields #22600
• The type for a readonly T x; record field needs to be set as T & readonly The type for a readonly T x; record field needs to be set as T & readonly #23257
• Identify and fix issues in xml<T> & readonly Identify and fix issues in xml<T> & readonly #23276