Support ProgramOptions to disable string conversion and list/string concatenation

[sergiitk]

Feature request checklist

• There are no issues that match the desired change
• The change is large enough it can't be addressed with a simple Pull Request
• If this is a bug, please file a Bug Report.

Change
To make CEL environment setup consistent across CEL implementations, I propose to add equivalent runtime options that control string conversion and list/string concatenation equivalent to those found in CEL-cpp:

// Enable string() overloads.
bool enable_string_conversion = true;

// Enable string concatenation overload.
bool enable_string_concat = true;

// Enable list concatenation overload.
bool enable_list_concat = true;

Example

// Actual option names up to the implementer.
opts := cel.EvalOptions(cel.OptDisableDisableStringConcat |
	cel.OptDisableDisableListConcat | cel.OptDisableDisableListConcat)
prg, err := env.Program(ast, opts)

Related

• Corresponding cel-java request: Support CelOptions to disable string conversion and list/string concatenation cel-java#502
• Internal ref: go/grpc-cel-integration