String functions for compile time

[antsok]

Is your feature request related to a problem? Please describe.
When working with bicep files and loading JSON/text content to be used as an input, we are performing some string replacement functions.

For example,

var customPolicies = string(loadJsonContent('../../inputs/policies.json'))
var customPoliciesModified1 = replace(customPolicies, "valueOld", "valueNew")
var customPoliciesModified = array(json(customPoliciesModified1))

Currently, this gets converted into ARM functions and increases the size of the deployment and with large JSONs and many replaces it hits ARM limit on string literals in ARM template expressions.

Describe the solution you'd like
A way to apply string functions at a compile time.

[WhitWaldo]

Related to #444