[fuzz-utils] Add StringMap (4/4: clear,erase)

This CL adds the clear and erase methods to StringMap to allow
callers to remove elements from the map.

SEC-103

Tests: Added more fuzz-utils unit tests.

Change-Id: I0a33854665fba4d4220d7909d80cb89671bc26d3

[fuzz-utils] Add StringMap (3/4: begin,next)

This CL adds the begin and next method to StringMap. These allow
callers to iterate over the key-value pairs of the map.

SEC-103

Tests: Added more fuzz-utils unit tests.
Change-Id: I2d94ef8f09b6b7610f5190a1e068ea6327c7b706

[fuzz-utils] Add StringMap (2/4: get,set)

This CL adds method to StringMap to store and retrieve C-style
strings from the associative container.

SEC-103

Tests: Added more fuzz-utils unit tests.
Change-Id: Id711de7b1cd316f7ca8ed6e9c135241dab294c20

[fuzz-utils] Add StringMap (1/4: basic getters)

This CL adds the skeleton of StringMap, an assoicative container for
for managing C-style strings in a fbl::WAVLTree.

SEC-103

Tests: Added fuzz-utils unit tests.

Change-Id: Iaac788d412bfab1e573188a413cc3841d983f7b1

Change-Id: I167d4c77af2c7d3fc419540a9c9d38d76663744a