[Discussion] directive has ambiguous syntax

for where statement, following have ambiguous syntax
```
const subjectRegex = getPatternToMatch(directive.where.subject);
const subjectPrefixRegex = getPatternToMatch(directive.where['subject-prefix']);
const verbRegex = getPatternToMatch(directive.where.verb);
const variantRegex = getPatternToMatch(directive.where.variant);
const parameterRegex = getPatternToMatch(directive.where['parameter-name']);
const enumNameRegex = getPatternToMatch(directive.where['enum-name']);
const enumValueNameRegex = getPatternToMatch(directive.where['enum-value-name']);
const modelNameRegex = getPatternToMatch(directive.where['model-name']);
const modelFullNameRegex = getPatternToMatch(directive.where['model-fullname']);
const modelNamespaceRegex = getPatternToMatch(directive.where['model-namespace']);
const propertyNameRegex = getPatternToMatch(directive.where['property-name']);
```
the method "getPatternToMatch" treat "pattern" as /^pattern$/ and "pattern.*" as /pattern.*/
for a regex, /pattern/ has different meaning from /^pattern$/, autorest.powershell should not make such assumption.

We should treat all input as regex.