Normalize enum member name

[MaryGao]

fixes #2832
fixes #2958

Background

For generated enum we need enum member name and value, and the typespec member name may not be a valid typescript name so we need to normalize them and also normalization could help produce more ts-style SDKs.

Unlike property or model name enum member could be any chars e.g *&^-, so it would require more sanitize logic during normalization. And to be consistant I apply all these rules to other type normalization also. So we could see some breakings in model name and property.

Design consideration

• There is no perfect rule without knowing the context. From codegen side we would ensure the naming style is consistant and also ensure the generated code are compile-pass.
• If the name is starting with digital number or is a numeric literal name we will add Num prefix and report warning to remind renaming for customers
• We could disable normalization by turning on the option ignoreEnumMemberNameNormalize: true at package level
• We could bypass normalization with adding prefix $DO_NOT_NORMALIZE$ at member level, e.g $DO_NOT_NORMALIZE$VALIDATION_NOT_REQUIRED => VALIDATION_NOT_REQUIRED
• The breakings between HLC and modular should be limited, if existing we could leverage clientName or above prefix to avoid that
• The normalization would also impact other norm and for property the main impact would remove the special chars in property e.g $filter to filter

Cases

// case 1: pure alphabets
["pascal", "Pascal"],
["pascalCase", "PascalCase"],
["PascalCase", "PascalCase"],
["pascalcase", "Pascalcase"],
["Pascalcase", "Pascalcase"],

// case 2: alphabets + special chars e.g .-*/
["pascal_case", "PascalCase"],
["pascal_case_", "PascalCase"],
["_pascal_case", "PascalCase"],
["pascal, case", "PascalCase"],
["MAX_of_MLD", "MAXOfMld"],

// case 3: alphabets + special chars + digits
["___pascal____case6666", "PascalCase6666"],
["_10Min", "Num_10Min"],

// case 4: digits but not a numeric name
["090", "Num090"],

// case 5: digits but valid numeric name
["10", "Num10"],
["-1.1", "Num-1.1"],

Relevant issues

• [Bug]: How to locate/decorate union variant in union? microsoft/typespec#5081

[MaryGao]

need to keep this case.