Dpdk Backend: Enable header stack dynamic index elimination

[usha1830]

This PR enables midend pass HSIndexSimplifier to simplify header stack indices.
The dynamic index expression is replaced with series of if-statements with the dynamic index replaced with constant values based on the runtime value of index.

Tests added to cover the following expressions/statements

• Assignment statements (on both sides as well)
• Table keys
• If condition expression
• Switch expression
• Function param
• Binary operation
• Unary Operation
• Slice

[usha1830]

Fedora build is failing with this error

Error: fatal: unable to access 'https://github.com/p4lang/p4runtime.git/': Could not resolve host: github.com
 Unable to fetch in submodule path 'control-plane/p4runtime'; trying to directly fetch 7a322f35f0c80bf20bc7fcc96f9d1ab77e5fd07a:
 From https://github.com/p4lang/p4runtime
  * branch            7a322f35f0c80bf20bc7fcc96f9d1ab77e5fd07a -> FETCH_HEAD
 Submodule path 'control-plane/p4runtime': checked out '7a322f35f0c80bf20bc7fcc96f9d1ab77e5fd07a'
 Error: fatal: unable to access 'https://github.com/google/googletest.git/': Could not resolve host: github.com

[usha1830]

@mbudiu-vmw Could you please review this PR? This uses the midend pass HSIndexSimplifier for non-constant header stack index elimination.

The other PR which implements this transformation directly in DPDK backend is #3371. Please suggest if that should be used instead.