[fir] Add character utility functions in FIRBuilder

Extract part of D111337 in order to mke it smaller
and easier to review. This patch add some utility
functions to the FIRBuilder.

Add the following utility functions:
- getCharacterLengthType
- createStringLiteral
- locationToFilename
- characterWithDynamicLen
- sequenceWithNonConstantShape
- hasDynamicSize

These bring up the BoxValue implementation together with it.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: AlexisPerry

Differential Revision: https://reviews.llvm.org/D112074



Co-authored-by: Jean Perier <jperier@nvidia.com>
Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>