Implement procedural macro host generate_code for attribute macro

[maciektr]

Resolves #1127

commit-id:e59370d2

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Stack:

• Implement procedural macro diagnostics #1159
• Split cairo-lang-macro crate into two (api <> abi) #1157
• Add aux_data to proc macro result #1143
• Use json output format in cargo if set in scarb_ui #1151
• Run cargo fetch on workspace resolve #1150
• Implement check command for cairo plugins #1148
• Add test case for procedural macro compilation #1100
• Change compilation unit to enum #1155
• Procedural macro compilation #1110
• Implement loading shared libraries for proc macro plugins #1093
• Implement procedural macro host generate_code for attribute macro #1091 ⬅

⚠️ Part of a stack created by spr. Do not merge manually using the UI - doing so may have unexpected results.

[piotmag769]

I assume TODO's are done later in the PR stack, right?

I noticed that the TokenStream is a simple String rn, we want to change it to be an iterator over tokens later on, right?

After digging into the code - LGTM